ns2: Accept NS-UNBLOCK-ACK in UNBLOCKED state

if we transition to UNBLOCKED as a result of a locally-generated
unblock action, then of course we will receive an inbound UNBLOCK-ACK.

Let's avoid error log messages and confusign the peer with NS-STATUS
in this case:

DLNS DEBUG GPRS-NS2-VC(FR-hdlcnet3-DLCI18-NSEI2001-NSVCI3)[0x612000001720]{UNBLOCKED}: Received Event UNBLOCK_ACK (gprs_ns2_vc_fsm.c:692)
DLNS ERROR GPRS-NS2-VC(FR-hdlcnet3-DLCI18-NSEI2001-NSVCI3)[0x612000001720]{UNBLOCKED}: Event UNBLOCK_ACK not permitted (gprs_ns2_vc_fsm.c:692)

Change-Id: Icc4d960ddad82e3ebbf571d8ff9f24854b52a946
diff --git a/src/gb/gprs_ns2_vc_fsm.c b/src/gb/gprs_ns2_vc_fsm.c
index 08b6b2d..0f6eeab 100644
--- a/src/gb/gprs_ns2_vc_fsm.c
+++ b/src/gb/gprs_ns2_vc_fsm.c
@@ -400,7 +400,7 @@
 		.onenter = gprs_ns2_st_blocked_onenter,
 	},
 	[GPRS_NS2_ST_UNBLOCKED] = {
-		.in_event_mask = S(GPRS_NS2_EV_BLOCK),
+		.in_event_mask = S(GPRS_NS2_EV_BLOCK) | S(GPRS_NS2_EV_UNBLOCK_ACK),
 		.out_state_mask = S(GPRS_NS2_ST_RESET) | S(GPRS_NS2_ST_ALIVE) |
 				  S(GPRS_NS2_ST_BLOCKED) |
 				  S(GPRS_NS2_ST_UNCONFIGURED),