Add Osmux IPv6 support

A new osmux bind-ip-v6 VTY command is added, similar to what's already
available for RTP. This way the user can decide whether to support IPv4,
IPv6 or both types of IP versions.

Both IP sockets are by default disabled, and must be explicitly enabled
by setting the bind-ip in the VTY configuration.

Change-Id: I446cd7da217e9f4a74995d7784ae55dcc60a29b7
diff --git a/include/osmocom/mgcp/mgcp_network.h b/include/osmocom/mgcp/mgcp_network.h
index 349ff94..a3d57f0 100644
--- a/include/osmocom/mgcp/mgcp_network.h
+++ b/include/osmocom/mgcp/mgcp_network.h
@@ -157,7 +157,7 @@
 			  struct mgcp_rtp_state *state,
 			  struct mgcp_rtp_end *rtp_end,
 			  struct osmo_sockaddr *addr, struct msgb *msg);
-void mgcp_get_local_addr(char *addr, struct mgcp_conn_rtp *conn);
+int mgcp_get_local_addr(char *addr, struct mgcp_conn_rtp *conn);
 
 /* payload processing default functions */
 int mgcp_rtp_processing_default(struct mgcp_endpoint *endp, struct mgcp_rtp_end *dst_end,