refactor(rust/trezor-thp): minor tweaks

diff --git a/rust/trezor-thp/src/channel/buffered.rs b/rust/trezor-thp/src/channel/buffered.rs
index 030cfba7..9ed591b3 100644
--- a/rust/trezor-thp/src/channel/buffered.rs
+++ b/rust/trezor-thp/src/channel/buffered.rs
@@ -29,6 +29,10 @@ impl<C: ChannelIO> Buffered<C> {
         }
     }
 
+    pub fn packet_len(&self) -> usize {
+        self.packet_len
+    }
+
     pub fn set_packet_len(&mut self, packet_len: usize) {
         self.packet_len = packet_len;
     }
diff --git a/rust/trezor-thp/src/channel/device.rs b/rust/trezor-thp/src/channel/device.rs
index fb2a2b58..44ab9949 100644
--- a/rust/trezor-thp/src/channel/device.rs
+++ b/rust/trezor-thp/src/channel/device.rs
@@ -270,6 +270,10 @@ where
     fn message_retransmit(&mut self) -> Result<(), Error> {
         Ok(())
     }
+
+    fn channel_id(&self) -> u16 {
+        BROADCAST_CHANNEL_ID
+    }
 }
 
 #[derive(Copy, Clone)]
@@ -451,10 +455,6 @@ impl<C: CredentialVerifier, B: Backend> ChannelOpen<C, B> {
         })
     }
 
-    pub fn channel_id(&self) -> u16 {
-        self.channel.channel_id
-    }
-
     pub fn sending_retry(&self) -> Option<u8> {
         self.channel.sending_retry()
     }
@@ -555,6 +555,10 @@ where
     fn message_retransmit(&mut self) -> Result<(), Error> {
         self.channel.message_retransmit()
     }
+
+    fn channel_id(&self) -> u16 {
+        self.channel.channel_id()
+    }
 }
 
 /// Helper for assigning consecutive channel IDs.
diff --git a/rust/trezor-thp/src/channel/host.rs b/rust/trezor-thp/src/channel/host.rs
index 4ab7312f..a1280ecb 100644
--- a/rust/trezor-thp/src/channel/host.rs
+++ b/rust/trezor-thp/src/channel/host.rs
@@ -315,6 +315,10 @@ where
     fn message_retransmit(&mut self) -> Result<(), Error> {
         Ok(())
     }
+
+    fn channel_id(&self) -> u16 {
+        BROADCAST_CHANNEL_ID
+    }
 }
 
 #[derive(Copy, Clone)]
@@ -491,10 +495,6 @@ impl<C: CredentialStore, B: Backend> ChannelOpen<C, B> {
         })
     }
 
-    pub fn channel_id(&self) -> u16 {
-        self.channel.channel_id
-    }
-
     pub fn sending_retry(&self) -> Option<u8> {
         self.channel.sending_retry()
     }
@@ -581,4 +581,8 @@ where
     fn message_retransmit(&mut self) -> Result<(), Error> {
         self.channel.message_retransmit()
     }
+
+    fn channel_id(&self) -> u16 {
+        self.channel.channel_id()
+    }
 }
diff --git a/rust/trezor-thp/src/channel/mod.rs b/rust/trezor-thp/src/channel/mod.rs
index b7348d91..f0c93325 100644
--- a/rust/trezor-thp/src/channel/mod.rs
+++ b/rust/trezor-thp/src/channel/mod.rs
@@ -70,6 +70,7 @@ impl Nonce {
 }
 
 /// Sent by device after successful handshake to indicate whether pairing is required.
+#[cfg_attr(any(test, debug_assertions), derive(Debug))]
 #[repr(u8)]
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum PairingState {
@@ -157,6 +158,7 @@ enum ReceiveState<R: Role> {
 /// encrypted transport phase can also use protobuf messages, their meaning is generally
 /// different than in the other phases.
 /// Application can use this enum to distinguish the context.
+#[cfg_attr(any(test, debug_assertions), derive(Debug))]
 #[repr(u8)]
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum Phase {
@@ -207,10 +209,6 @@ impl<R: Role, B: Backend> Channel<R, B> {
         self.noise.as_mut().ok_or_else(Error::unexpected_input)
     }
 
-    pub fn channel_id(&self) -> u16 {
-        self.channel_id
-    }
-
     pub fn handshake_hash(&self) -> &[u8; HANDSHAKE_HASH_LEN] {
         self.noise.as_ref().unwrap().handshake_hash()
     }
@@ -762,6 +760,9 @@ pub trait ChannelIO {
         send_buffer[3..plaintext_len].copy_from_slice(message);
         self.message_in(plaintext_len, send_buffer)
     }
+
+    /// Get channel identifier, or `BROADCAST_CHANNEL_ID` for muxes.
+    fn channel_id(&self) -> u16;
 }
 
 impl<R: Role, B: Backend> ChannelIO for Channel<R, B> {
@@ -900,6 +901,10 @@ impl<R: Role, B: Backend> ChannelIO for Channel<R, B> {
         *retry = retry.saturating_add(1);
         Ok(())
     }
+
+    fn channel_id(&self) -> u16 {
+        self.channel_id
+    }
 }
 
 /// The maximum number of transport payload retransmissions that the sender should attempt.
diff --git a/rust/trezor-thp/src/channel/test.rs b/rust/trezor-thp/src/channel/test.rs
index 496fd10c..8165e367 100644
--- a/rust/trezor-thp/src/channel/test.rs
+++ b/rust/trezor-thp/src/channel/test.rs
@@ -47,9 +47,10 @@ const DEVICE_KEY: &[u8; PRIVKEY_LEN] = &[0u8; PRIVKEY_LEN];
 const DEVICE_PROPERTIES: &[u8] =
     b"\x0a\x04\x54\x32\x57\x31\x10\x00\x18\x02\x20\x00\x28\x02\x28\x01";
 
+// Set environment variable RUST_LOG=<level> to enable logging, e.g. RUST_LOG=trace.
 fn setup() {
     SETUP.call_once(|| {
-        env_logger::init_from_env(env_logger::Env::default().filter_or("RUST_LOG", "info"));
+        env_logger::init_from_env(env_logger::Env::default().filter_or("RUST_LOG", "off"));
     })
 }
 
@@ -120,6 +121,10 @@ impl<C: CredentialVerifier, B: Backend> ChannelIO for WithKey<C, B> {
     fn message_retransmit(&mut self) -> Result<()> {
         self.channel.message_retransmit()
     }
+
+    fn channel_id(&self) -> u16 {
+        self.channel.channel_id()
+    }
 }
 
 impl<C: CredentialVerifier, B: Backend> Deref for WithKey<C, B> {
diff --git a/rust/trezor-thp/src/lib.rs b/rust/trezor-thp/src/lib.rs
index edd42338..07b3bba4 100644
--- a/rust/trezor-thp/src/lib.rs
+++ b/rust/trezor-thp/src/lib.rs
@@ -4,7 +4,7 @@
 
 mod alternating_bit;
 pub mod channel;
-mod control_byte;
+pub mod control_byte;
 mod crc32;
 pub mod credential;
 pub mod error;