ipa: Make a reservation for the GSUP protocol

GSUP is a protocol to have the OpenBSC SGSN talk
to an exterbal system for 3GPP MAP connectivity.
diff --git a/include/osmocom/gsm/protocol/ipaccess.h b/include/osmocom/gsm/protocol/ipaccess.h
index 3de0ce1..f98ebd6 100644
--- a/include/osmocom/gsm/protocol/ipaccess.h
+++ b/include/osmocom/gsm/protocol/ipaccess.h
@@ -34,6 +34,7 @@
 	IPAC_PROTO_EXT_LAC	= 0x02,
 	IPAC_PROTO_EXT_SMSC	= 0x03,
 	IPAC_PROTO_EXT_ORC	= 0x04,		/* OML Router Control */
+	IPAC_PROTO_EXT_GSUP	= 0x05,		/* GSUP GPRS extension */
 };
 
 enum ipaccess_msgtype {