gprs_ns2_sns: add missing S() to allow GPRS_SNS_EV_NO_NSVC happen

The event GPRS_SNS_EV_NO_NSVC was never dispatched because the
S() was missing to convert it into a bitmask.

Change-Id: I4af01293ff0ba8629e1426b1ba92f72f0520c7f0
diff --git a/src/gb/gprs_ns2_sns.c b/src/gb/gprs_ns2_sns.c
index 50a1f9b..edf7da3 100644
--- a/src/gb/gprs_ns2_sns.c
+++ b/src/gb/gprs_ns2_sns.c
@@ -1205,7 +1205,7 @@
 	.name = "GPRS-NS2-SNS-BSS",
 	.states = ns2_sns_bss_states,
 	.num_states = ARRAY_SIZE(ns2_sns_bss_states),
-	.allstate_event_mask = GPRS_SNS_EV_NO_NSVC,
+	.allstate_event_mask = S(GPRS_SNS_EV_NO_NSVC),
 	.allstate_action = ns2_sns_st_all_action,
 	.cleanup = NULL,
 	.timer_cb = ns2_sns_fsm_bss_timer_cb,