[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/include/net/dst.h b/include/net/dst.h
index e9ff4a4..2f65e89 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -143,6 +143,13 @@
 	atomic_inc(&dst->__refcnt);
 }
 
+static inline void dst_use(struct dst_entry *dst, unsigned long time)
+{
+	dst_hold(dst);
+	dst->__use++;
+	dst->lastuse = time;
+}
+
 static inline
 struct dst_entry * dst_clone(struct dst_entry * dst)
 {