[NET]: Make helper to get dst entry and "use" it

There are many places that get the dst entry, increase the
__use counter and set the "lastuse" time stamp.

Make a helper for this.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index c95b270..4565183 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -851,9 +851,7 @@
 			 */
 			rcu_assign_pointer(rt_hash_table[hash].chain, rth);
 
-			rth->u.dst.__use++;
-			dst_hold(&rth->u.dst);
-			rth->u.dst.lastuse = now;
+			dst_use(&rth->u.dst, now);
 			spin_unlock_bh(rt_hash_lock_addr(hash));
 
 			rt_drop(rt);
@@ -1930,9 +1928,7 @@
 		    rth->fl.oif == 0 &&
 		    rth->fl.mark == skb->mark &&
 		    rth->fl.fl4_tos == tos) {
-			rth->u.dst.lastuse = jiffies;
-			dst_hold(&rth->u.dst);
-			rth->u.dst.__use++;
+			dst_use(&rth->u.dst, jiffies);
 			RT_CACHE_STAT_INC(in_hit);
 			rcu_read_unlock();
 			skb->dst = (struct dst_entry*)rth;
@@ -2326,9 +2322,7 @@
 		    rth->fl.mark == flp->mark &&
 		    !((rth->fl.fl4_tos ^ flp->fl4_tos) &
 			    (IPTOS_RT_MASK | RTO_ONLINK))) {
-			rth->u.dst.lastuse = jiffies;
-			dst_hold(&rth->u.dst);
-			rth->u.dst.__use++;
+			dst_use(&rth->u.dst, jiffies);
 			RT_CACHE_STAT_INC(out_hit);
 			rcu_read_unlock_bh();
 			*rp = rth;