BSSGP: do not reject SUSPEND ACK / NACK messages

Both BSSGP SUSPEND ACK and NACK messages use BVCI=0 (signaling),
which always exists. Claiming that BVCI=0 is unknown is wrong.

Instead of adding both BSSGP_PDUT_SUSPEND_{ACK,NACK} to the 'if'
statement, let's rather avoid rejection for all BVCI=0 messages,
as there may be other unlisted message types.

Change-Id: I780657c1e8f67e0bef0e92a31db7ba61b57d7ec4
Related: OS#4111
diff --git a/src/gprs_bssgp_pcu.cpp b/src/gprs_bssgp_pcu.cpp
index abcb106..f99058a 100644
--- a/src/gprs_bssgp_pcu.cpp
+++ b/src/gprs_bssgp_pcu.cpp
@@ -407,10 +407,7 @@
 	/* look-up or create the BTS context for this BVC */
 	bctx = btsctx_by_bvci_nsei(ns_bvci, msgb_nsei(msg));
 
-	if (!bctx
-	 && pdu_type != BSSGP_PDUT_BVC_RESET_ACK
-	 && pdu_type != BSSGP_PDUT_BVC_UNBLOCK_ACK
-	 && pdu_type != BSSGP_PDUT_PAGING_PS)
+	if (!bctx && ns_bvci != BVCI_SIGNALLING)
 	{
 		LOGP(DBSSGP, LOGL_NOTICE, "NSEI=%u/BVCI=%u Rejecting PDU type %s for unknown BVCI\n",
 		     nsei, ns_bvci, bssgp_pdu_str(pdu_type));