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_mgcp_utils.c b/openbsc/src/nat/bsc_mgcp_utils.c
index dc8cd81..aacfce6 100644
--- a/openbsc/src/nat/bsc_mgcp_utils.c
+++ b/openbsc/src/nat/bsc_mgcp_utils.c
@@ -303,7 +303,7 @@
 		}
 
 		/* send the message and a fake MDCX to force sending of a dummy packet */
-		bsc_write(sccp->bsc, bsc_msg, IPAC_PROTO_MGCP);
+		bsc_write(sccp->bsc, bsc_msg, IPAC_PROTO_MGCP_OLD);
 		bsc_mgcp_send_mdcx(sccp->bsc, sccp->bsc_endp, mgcp_endp);
 		return MGCP_POLICY_DEFER;
 	} else if (state == MGCP_ENDP_DLCX) {
@@ -312,7 +312,7 @@
 		bsc_mgcp_dlcx(sccp);
 		return MGCP_POLICY_CONT;
 	} else {
-		bsc_write(sccp->bsc, bsc_msg, IPAC_PROTO_MGCP);
+		bsc_write(sccp->bsc, bsc_msg, IPAC_PROTO_MGCP_OLD);
 		return MGCP_POLICY_DEFER;
 	}
 }