ipa: Only use one IPA number for Osmo extensions

Instead of using more numbers from the proto range we will
use the 0xee and then have a mini header with our new proto
id in there. For a start rename the use types to _OLD.
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index 05868f9..aba082d 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -262,7 +262,7 @@
 	msg->l3h = msgb_put(msg, length);
 	memcpy(msg->l3h, data, length);
 
-        return bsc_write(bsc, msg, IPAC_PROTO_MGCP);
+        return bsc_write(bsc, msg, IPAC_PROTO_MGCP_OLD);
 }
 
 int bsc_write(struct bsc_connection *bsc, struct msgb *msg, int proto)