NS_Emulation: Tolerate late NS-BLOCK-ACK / NS-UNBLOCK-ACK

Particularly in case both sides initiate a BLOCK or UNBLOCK procedure
at almost the same time, it can happen thet we're already in BLOCKED
state and receive a late BLOCK-ACK or in UNBLOCKED state and receive a
late UNBLOCK-ACK.

Let's just silently discard them instaed of generating NS-STATUS which
may confuse the peer.

Change-Id: I2e5b934e1cf6c6cf982d5ab1dbb32e8920b91071

library/NS_Emulation.ttcnpp

@@ -561,6 +561,9 @@ module NS_Emulation {
 			Tns_block.stop;
 			f_change_state(NSVC_S_ALIVE_UNBLOCKED);
 		}
+		/* tolerate a late NS-BLOCK-ACK from peer */
+		[] NSCP.receive(tr_NS_BLOCK_ACK(g_nsvc_config.nsvci)) -> value rf {
+		}
 		[] Tns_block.timeout {
 			/* repeat unblock transmission */
 			f_sendUnblock();
@@ -583,6 +586,9 @@ module NS_Emulation {
 		[] NSCP.receive(tr_NS_BLOCK_ACK(g_nsvc_config.nsvci)) -> value rf {
 			Tns_block.stop;
 		}
+		/* tolerate a late NS-UNBLOCK-ACK from peer */
+		[] NSCP.receive(t_NS_UNBLOCK_ACK) -> value rf {
+		}
 		/* NS-UNITDATA PDU from network to NS-UNITDATA.ind to user */
 		[] NSCP.receive(tr_NS_UNITDATA(?, ?, ?)) -> value rf {
 			NS_SP.send(ts_NsUdInd(g_config.nsei, g_nsvc_config.nsvci,