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/bsc/osmo_bsc_msc.c b/openbsc/src/bsc/osmo_bsc_msc.c
index 8b23c6f..b0c0044 100644
--- a/openbsc/src/bsc/osmo_bsc_msc.c
+++ b/openbsc/src/bsc/osmo_bsc_msc.c
@@ -67,7 +67,7 @@
         }
 
 	mgcp->l2h = msgb_put(mgcp, ret);
-	msc_queue_write(data->msc_con, mgcp, IPAC_PROTO_MGCP);
+	msc_queue_write(data->msc_con, mgcp, IPAC_PROTO_MGCP_OLD);
 	return 0;
 }
 
@@ -223,7 +223,7 @@
 		}
 	} else if (hh->proto == IPAC_PROTO_SCCP) {
 		sccp_system_incoming(msg);
-	} else if (hh->proto == IPAC_PROTO_MGCP) {
+	} else if (hh->proto == IPAC_PROTO_MGCP_OLD) {
 		mgcp_forward(data, msg);
 	}