batman-adv: dat: fix tie-break for candidate selection

The original version of the candidate selection for DAT attempted to
compare both candidate and max_orig_node to identify which has the smaller
MAC address. This comparison is required as tie-break when a hash collision
happened.

But the used function returned 0 when the function was not equal and a
non-zero value when it was equal. As result, the actually selected
node was dependent on the order of entries in the orig_hash and not
actually on the mac addresses. The last originator in the hash collision
would always win.

To have a proper ordering, it must diff the actual MAC address bytes and
reject the candidate when the diff is not smaller than 0.

Cc: stable@vger.kernel.org
Fixes: 785ea11441 ("batman-adv: Distributed ARP Table - create DHT helper functions")
Signed-off-by: Sven Eckelmann <sven@narfation.org>

net/batman-adv/distributed-arp-table.c

@@ -546,7 +546,7 @@ static bool batadv_is_orig_node_eligible(struct batadv_dat_candidate *res,
 	 * the one with the lowest address
 	 */
 	if (tmp_max == max && max_orig_node &&
-	    batadv_compare_eth(candidate->orig, max_orig_node->orig))
+	    memcmp(candidate->orig, max_orig_node->orig, ETH_ALEN) >= 0)
 		goto out;
 
 	ret = true;