nat: If the number starts with 00 turn it into a international number

Switch the type to international and skip the '00' of the phone
number. This should fix some issues with gateway MSCs.
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index b43d67a..7b75fa5 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -848,7 +848,12 @@
 	memcpy(outptr, &hdr48->data[0], sec_len);
 
 	/* create the new number */
-	strncpy(called.number, new_number, sizeof(called.number));
+	if (strncmp(new_number, "00", 2) == 0) {
+		called.type = 1;
+		strncpy(called.number, new_number + 2, sizeof(called.number));
+	} else {
+		strncpy(called.number, new_number, sizeof(called.number));
+	}
 	gsm48_encode_called(out, &called);
 
 	/* copy thre rest */