lnwire: let gossip messages implement GossipMessage

diff --git a/lnwire/announcement_signatures.go b/lnwire/announcement_signatures.go
index cf8f68b..29ada70 100644
--- a/lnwire/announcement_signatures.go
+++ b/lnwire/announcement_signatures.go
@@ -121,3 +121,10 @@ func (a *AnnounceSignatures1) SCID() ShortChannelID {
 func (a *AnnounceSignatures1) ChanID() ChannelID {
 	return a.ChannelID
 }
+
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (a *AnnounceSignatures1) GossipVersion() GossipVersion {
+	return GossipVersion1
+}
diff --git a/lnwire/announcement_signatures_2.go b/lnwire/announcement_signatures_2.go
index 04e4c0a..a2806f1 100644
--- a/lnwire/announcement_signatures_2.go
+++ b/lnwire/announcement_signatures_2.go
@@ -102,6 +102,13 @@ func (a *AnnounceSignatures2) MsgType() MessageType {
 	return MsgAnnounceSignatures2
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (a *AnnounceSignatures2) GossipVersion() GossipVersion {
+	return GossipVersion2
+}
+
 // SerializedSize returns the serialized size of the message in bytes.
 //
 // This is part of the lnwire.SizeableMessage interface.
diff --git a/lnwire/channel_announcement.go b/lnwire/channel_announcement.go
index 05161cc..cab8407 100644
--- a/lnwire/channel_announcement.go
+++ b/lnwire/channel_announcement.go
@@ -232,6 +232,13 @@ func (a *ChannelAnnouncement1) SCID() ShortChannelID {
 	return a.ShortChannelID
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (a *ChannelAnnouncement1) GossipVersion() GossipVersion {
+	return GossipVersion1
+}
+
 // A compile-time check to ensure that ChannelAnnouncement1 implements the
 // ChannelAnnouncement interface.
 var _ ChannelAnnouncement = (*ChannelAnnouncement1)(nil)
diff --git a/lnwire/channel_announcement_2.go b/lnwire/channel_announcement_2.go
index a82624a..9227584 100644
--- a/lnwire/channel_announcement_2.go
+++ b/lnwire/channel_announcement_2.go
@@ -307,6 +307,13 @@ func (c *ChannelAnnouncement2) SCID() ShortChannelID {
 	return c.ShortChannelID.Val
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (c *ChannelAnnouncement2) GossipVersion() GossipVersion {
+	return GossipVersion2
+}
+
 // A compile-time check to ensure that ChannelAnnouncement2 implements the
 // ChannelAnnouncement interface.
 var _ ChannelAnnouncement = (*ChannelAnnouncement2)(nil)
diff --git a/lnwire/channel_update.go b/lnwire/channel_update.go
index 2dc4a11..09b8044 100644
--- a/lnwire/channel_update.go
+++ b/lnwire/channel_update.go
@@ -363,6 +363,13 @@ func (a *ChannelUpdate1) ForwardingPolicy() *ForwardingPolicy {
 	}
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (a *ChannelUpdate1) GossipVersion() GossipVersion {
+	return GossipVersion1
+}
+
 // CmpAge can be used to determine if the update is older or newer than the
 // passed update. It returns 1 if this update is newer, -1 if it is older, and
 // 0 if they are the same age.
diff --git a/lnwire/channel_update_2.go b/lnwire/channel_update_2.go
index 7fe7670..8e82fe9 100644
--- a/lnwire/channel_update_2.go
+++ b/lnwire/channel_update_2.go
@@ -85,6 +85,13 @@ type ChannelUpdate2 struct {
 	ExtraSignedFields
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (c *ChannelUpdate2) GossipVersion() GossipVersion {
+	return GossipVersion2
+}
+
 // Encode serializes the target ChannelUpdate2 into the passed io.Writer
 // observing the protocol version specified.
 //
diff --git a/lnwire/interfaces.go b/lnwire/interfaces.go
index 64d87f7..115b07d 100644
--- a/lnwire/interfaces.go
+++ b/lnwire/interfaces.go
@@ -45,6 +45,7 @@ type AnnounceSignatures interface {
 	ChanID() ChannelID
 
 	Message
+	GossipMessage
 }
 
 // ChannelAnnouncement is an interface that must be satisfied by any message
@@ -66,6 +67,7 @@ type ChannelAnnouncement interface {
 	Node2KeyBytes() [33]byte
 
 	Message
+	GossipMessage
 }
 
 // CompareResult represents the result after comparing two things.
@@ -122,6 +124,7 @@ type ChannelUpdate interface {
 	SetSCID(scid ShortChannelID)
 
 	Message
+	GossipMessage
 }
 
 // NodeAnnouncement is an interface that must be satisfied by any message used
@@ -138,6 +141,7 @@ type NodeAnnouncement interface {
 	TimestampDesc() string
 
 	Message
+	GossipMessage
 }
 
 // ForwardingPolicy defines the set of forwarding constraints advertised in a
diff --git a/lnwire/node_announcement.go b/lnwire/node_announcement.go
index 384327f..468ac79 100644
--- a/lnwire/node_announcement.go
+++ b/lnwire/node_announcement.go
@@ -243,3 +243,10 @@ func (a *NodeAnnouncement1) NodeFeatures() *FeatureVector {
 func (a *NodeAnnouncement1) TimestampDesc() string {
 	return fmt.Sprintf("timestamp=%d", a.Timestamp)
 }
+
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (a *NodeAnnouncement1) GossipVersion() GossipVersion {
+	return GossipVersion1
+}
diff --git a/lnwire/node_announcement_2.go b/lnwire/node_announcement_2.go
index 0b7142d..93a3792 100644
--- a/lnwire/node_announcement_2.go
+++ b/lnwire/node_announcement_2.go
@@ -221,6 +221,13 @@ func (n *NodeAnnouncement2) TimestampDesc() string {
 	return fmt.Sprintf("block_height=%d", n.BlockHeight.Val)
 }
 
+// GossipVersion returns the gossip version that this message is part of.
+//
+// NOTE: this is part of the GossipMessage interface.
+func (n *NodeAnnouncement2) GossipVersion() GossipVersion {
+	return GossipVersion2
+}
+
 // A compile-time check to ensure NodeAnnouncement2 implements the Message
 // interface.
 var _ Message = (*NodeAnnouncement2)(nil)