nat: Allow to rewrite any non international number

Remove the arteficial limitation of the number format
of an unknown number.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
index 4696bb0..76b56f6 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat_utils.c
@@ -811,8 +811,6 @@
 		return NULL;
 	if (called->type == 1)
 		return NULL;
-	if (strncmp(called->number, "00", 2) == 0)
-		return NULL;
 
 	/* need to find a replacement and then fix it */
 	llist_for_each_entry(entry, &nat->num_rewr->entry, list) {