fix strncpy bug in gprs_ns2_fr_bind()

This use of strncpy() fails to account for the terminating nul
character. Use OSMO_STRLCPY_ARRAY() instead.

(Interestingly my compiler doesn't complain about this one, though it
failed on another similar use of strncpy().)

Change-Id: Id53e940c7a39ab154966548f4173a179c5bc9151
diff --git a/src/gb/gprs_ns2_fr.c b/src/gb/gprs_ns2_fr.c
index 1ff80ed..782e5a3 100644
--- a/src/gb/gprs_ns2_fr.c
+++ b/src/gb/gprs_ns2_fr.c
@@ -497,7 +497,7 @@
 		rc = -EINVAL;
 		goto err_priv;
 	}
-	strncpy(priv->netif, netif, sizeof(priv->netif));
+	OSMO_STRLCPY_ARRAY(priv->netif, netif);
 
 	if (result)
 		*result = bind;