GMM: dont reply to GMM_DETACH_REQ with POWER OFF when MS is unknown

Change-Id: I1d1cf64500f1295ab58d157d4d4dab16fcddbbf3
diff --git a/src/gprs/gprs_gmm.c b/src/gprs/gprs_gmm.c
index 28fba71..93d64a4 100644
--- a/src/gprs/gprs_gmm.c
+++ b/src/gprs/gprs_gmm.c
@@ -1933,6 +1933,13 @@
 		if (gh->msg_type == GSM48_MT_GMM_DETACH_ACK)
 			return gprs_llgmm_unassign(llme);
 
+		/* Don't reply to deatch requests, reason power off */
+		if (gh->msg_type == GSM48_MT_GMM_DETACH_REQ &&
+			gh->data[0] & 0x8) {
+			return 0;
+		}
+
+
 		gprs_llgmm_reset(llme);
 
 		/* Don't force it into re-attachment */