common: export helper membuf_tal_realloc.

diff --git a/common/msg_queue.c b/common/msg_queue.c
index 566bb3bf..091b8380 100644
--- a/common/msg_queue.c
+++ b/common/msg_queue.c
@@ -2,6 +2,7 @@
 #include <ccan/membuf/membuf.h>
 #include <common/daemon.h>
 #include <common/msg_queue.h>
+#include <common/utils.h>
 #include <wire/wire.h>
 
 static bool warned_once;
@@ -33,21 +34,11 @@ static void destroy_msg_queue(struct msg_queue *q)
 	}
 }
 
-/* Realloc helper for tal membufs */
-static void *membuf_tal_realloc(struct membuf *mb, void *rawelems,
-				size_t newsize)
-{
-	char *p = rawelems;
-
-	tal_resize(&p, newsize);
-	return p;
-}
-
 struct msg_queue *msg_queue_new(const tal_t *ctx, bool fd_passing)
 {
 	struct msg_queue *q = tal(ctx, struct msg_queue);
 	q->fd_passing = fd_passing;
-	membuf_init(&q->mb, tal_arr(q, const u8 *, 0), 0, membuf_tal_realloc);
+	membuf_init(&q->mb, tal_arr(q, const u8 *, 0), 0, membuf_tal_resize);
 
 	if (q->fd_passing)
 		tal_add_destructor(q, destroy_msg_queue);
diff --git a/common/utils.c b/common/utils.c
index 01047ea5..e467c19d 100644
--- a/common/utils.c
+++ b/common/utils.c
@@ -194,3 +194,13 @@ char *str_lowering(const void *ctx, const char *string TAKES)
 	for (char *p = ret; *p; p++) *p = tolower(*p);
 	return ret;
 }
+
+/* Realloc helper for tal membufs */
+void *membuf_tal_resize(struct membuf *mb, void *rawelems, size_t newsize)
+{
+	char *p = rawelems;
+
+	tal_resize(&p, newsize);
+	return p;
+}
+
diff --git a/common/utils.h b/common/utils.h
index 45b91f87..a4f3ed97 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -8,8 +8,8 @@
 #include <ccan/tal/tal.h>
 #include <secp256k1.h>
 
+struct membuf;
 extern secp256k1_context *secp256k1_ctx;
-
 extern const struct chainparams *chainparams;
 
 /* Unsigned min/max macros: BUILD_ASSERT make sure types are unsigned */
@@ -163,6 +163,9 @@ extern const tal_t *wally_tal_ctx;
  * Returns created temporary path name at *created if successful. */
 int tmpdir_mkstemp(const tal_t *ctx, const char *template TAKES, char **created);
 
+/* For use with membuf_init */
+void *membuf_tal_resize(struct membuf *mb, void *rawelems, size_t newsize);
+
 /**
  * tal_strlowering - return the same string by in lower case.
  * @ctx: the context to tal from (often NULL)
diff --git a/plugins/libplugin.c b/plugins/libplugin.c
index 5b5c2f4e..836e1768 100644
--- a/plugins/libplugin.c
+++ b/plugins/libplugin.c
@@ -538,16 +538,6 @@ struct json_out *json_out_obj(const tal_t *ctx,
 	return jout;
 }
 
-/* Realloc helper for tal membufs */
-static void *membuf_tal_realloc(struct membuf *mb, void *rawelems,
-				size_t newsize)
-{
-	char *p = rawelems;
-
-	tal_resize(&p, newsize);
-	return p;
-}
-
 static int read_json_from_rpc(struct plugin *p)
 {
 	char *end;
@@ -1597,7 +1587,7 @@ static struct command_result *handle_init(struct command *cmd,
 			with_rpc = true;
 
 		membuf_init(&p->rpc_conn->mb, tal_arr(p, char, READ_CHUNKSIZE),
-			    READ_CHUNKSIZE, membuf_tal_realloc);
+			    READ_CHUNKSIZE, membuf_tal_resize);
 	} else
 		with_rpc = false;