NS_Emulation: Handle NS_PROV_LINK_STATUS_DOWN

This happens e.g. if FrameRelay detects a "service affecting condition",
i.e. the link is considered dead.

Change-Id: I7409079f5e2b77cc08ccc93d1b0baa72720cefb8
diff --git a/library/NS_Provider_FR.ttcn b/library/NS_Provider_FR.ttcn
index 1cb02dd..5138d82 100644
--- a/library/NS_Provider_FR.ttcn
+++ b/library/NS_Provider_FR.ttcn
@@ -62,6 +62,7 @@
 			}
 		[] FR.receive(FRemu_Event:{link_status:=FR_LINK_STS_UNAVAILABLE}) -> value rx_frevt {
 			link_available := false;
+			pvc_active := false;
 			NSE.send(NS_Provider_Evt:{link_status := NS_PROV_LINK_STATUS_DOWN});
 			}
 		[] FR.receive(tr_FRemu_PvcStatusAct(config.provider.fr.dlci, true)) -> value rx_frevt {