neigh: fix ARP retransmit timer guard

In commit 19e16d22 ("neigh: support smaller retrans_time settting")
we add more accurate control for ARP and NS. But for ARP I forgot to
update the latest guard in neigh_timer_handler(), then the next
retransmit would be reset to jiffies + HZ/2 if we set the retrans_time
less than 500ms. Fix it by setting the time_before() check to HZ/100.

IPv6 does not have this issue.
Reported-by: Jianwen Ji <jiji@redhat.com>
Fixes: 19e16d22 ("neigh: support smaller retrans_time settting")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -1082,8 +1082,8 @@ static void neigh_timer_handler(struct timer_list *t)
 	}
 
 	if (neigh->nud_state & NUD_IN_TIMER) {
-		if (time_before(next, jiffies + HZ/2))
-			next = jiffies + HZ/2;
+		if (time_before(next, jiffies + HZ/100))
+			next = jiffies + HZ/100;
 		if (!mod_timer(&neigh->timer, next))
 			neigh_hold(neigh);
 	}