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_filter.c b/openbsc/src/nat/bsc_filter.c
index f22f5be..73e9878 100644
--- a/openbsc/src/nat/bsc_filter.c
+++ b/openbsc/src/nat/bsc_filter.c
@@ -69,7 +69,7 @@
 	{ IPAC_PROTO_SCCP, ALLOW_ANY, ALLOW_ANY, ALLOW_ANY, FILTER_TO_BOTH },
 
 	/* allow MGCP messages to both sides */
-	{ IPAC_PROTO_MGCP, ALLOW_ANY, ALLOW_ANY, ALLOW_ANY, FILTER_TO_BOTH },
+	{ IPAC_PROTO_MGCP_OLD, ALLOW_ANY, ALLOW_ANY, ALLOW_ANY, FILTER_TO_BOTH },
 };
 
 struct bsc_nat_parsed *bsc_nat_parse(struct msgb *msg)