osmux: Rename function and pass msgb directly to it

The new prefix now matches other related functions acting on an osmux
connection.
Pass the msgb to it so simplify new msgb copy.

Change-Id: I8c0121485d0c96f70fe8bcbdb150793d428183ff
diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index 6edb4ae..3248cbd 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -1020,7 +1020,7 @@
 		LOGPENDP(endp, DRTP, LOGL_DEBUG,
 			 "endpoint type is MGCP_RTP_OSMUX, "
 			 "using osmux_xfrm_to_osmux() to forward data through OSMUX\n");
-		return osmux_xfrm_to_osmux((char*)msgb_data(msg), msgb_length(msg), conn_dst);
+		return conn_osmux_send_rtp(conn_dst, msg);
 	case MGCP_RTP_IUUP:
 		if (proto == MGCP_PROTO_RTP) {
 			LOGPENDP(endp, DRTP, LOGL_DEBUG,