gprs_ns2_sns: add missing transistion UNCONFIGURED -> SIZE

The SNS FSM can go into the SIZE state when all NS-VC are failing.
This is the case if the network connection to the SGSN got interrupted.

Change-Id: I7e7da9451458505c1c2d73836dd916aee7704fda
diff --git a/src/gb/gprs_ns2_sns.c b/src/gb/gprs_ns2_sns.c
index 31f8a5f..9091c9a 100644
--- a/src/gb/gprs_ns2_sns.c
+++ b/src/gb/gprs_ns2_sns.c
@@ -1169,7 +1169,8 @@
 		.in_event_mask = S(GPRS_SNS_EV_ADD) |
 				 S(GPRS_SNS_EV_DELETE) |
 				 S(GPRS_SNS_EV_CHANGE_WEIGHT),
-		.out_state_mask = S(GPRS_SNS_ST_UNCONFIGURED),
+		.out_state_mask = S(GPRS_SNS_ST_UNCONFIGURED) |
+				  S(GPRS_SNS_ST_SIZE),
 		.name = "CONFIGURED",
 		.action = ns2_sns_st_configured,
 		.onenter = ns2_sns_st_configured_onenter,