ipv4: Fix again the time difference calculation

	Fix again the diff value in rt_bind_exception
after collision of two latest patches, my original commit
actually fixed the same problem.
Signed-off-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -1926,7 +1926,7 @@ static void rt_bind_exception(struct rtable *rt, struct fib_nh *nh, __be32 daddr
 		if (daddr != fnhe_daddr)
 			continue;
 		if (pmtu) {
-			unsigned long diff = jiffies - expires;
+			unsigned long diff = expires - jiffies;
 
 			if (time_before(jiffies, expires)) {
 				rt->rt_pmtu = pmtu;