gprs-ns/test: Re-add return value check for gprs_nsvc_reset

The return value check has been removed in the commit 'Use
gprs_nsvc_reset instead of gprs_ns_tx_reset', because gprs_nsvc_reset
had no return value then. Since a compatible return value has been
added by 'Let gprs_nsvc_reset return a value', the former patch is
partly reverted by this commit.

The printf is now an OSMO_ASSERT. The commit message was taken
from Jacob.

Sponsored-by: On-Waves ehf
diff --git a/tests/gb/gprs_ns_test.c b/tests/gb/gprs_ns_test.c
index 2185ff8..500b40d 100644
--- a/tests/gb/gprs_ns_test.c
+++ b/tests/gb/gprs_ns_test.c
@@ -592,6 +592,7 @@
 	struct sockaddr_in peer[4] = {{0},};
 	struct gprs_nsvc *nsvc;
 	struct sockaddr_in *nse[4];
+	int rc;
 
 	peer[0].sin_family = AF_INET;
 	peer[0].sin_port = htons(1111);
@@ -641,7 +642,8 @@
 	printf("--- Setup VC 2 SGSN -> BSS (hits NSEI 2) ---\n\n");
 
 	nsvc = gprs_nsvc_by_nsvci(nsi, 0x2001);
-	gprs_nsvc_reset(nsvc, NS_CAUSE_OM_INTERVENTION);
+	rc = gprs_nsvc_reset(nsvc, NS_CAUSE_OM_INTERVENTION);
+	OSMO_ASSERT(rc < 0);
 
 	printf("--- Setup VC 1 SGSN -> BSS (hits NSEI 1) ---\n\n");