nat: First go at handling MGCP inside the nat

Listen on the MGCP gateway port and let our protocol stack
handle everything for now. We will need to have some more
control over things though.
diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index a5d3b1c..6f79106 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -142,6 +142,7 @@
 
 	/* MGCP config */
 	struct mgcp_config *mgcp_cfg;
+	struct write_queue mgcp_queue;
 };
 
 /* create and init the structures */
@@ -180,5 +181,6 @@
 int bsc_mgcp_assign(struct sccp_connections *, struct msgb *msg);
 void bsc_mgcp_clear(struct sccp_connections *);
 void bsc_mgcp_free_endpoints(struct bsc_nat *nat);
+int bsc_mgcp_init(struct bsc_nat *nat);
 
 #endif