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/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index f69a994..d75c01d 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -755,6 +755,12 @@
 	/* seed the PRNG */
 	srand(time(NULL));
 
+	/*
+	 * Setup the MGCP code..
+	 */
+	if (bsc_mgcp_init(nat) != 0)
+		return -4;
+
 	/* connect to the MSC */
 	msc_con = bsc_msc_create(msc_address, 5000);
 	if (!msc_con) {