mac80211: Revert 'Use correct sign for mesh active path refresh'

The patch ("mac80211: Use correct sign for mesh active path
refresh.") was actually a bug.  Reverted it and improved the
explanation of how mesh path refresh works.
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Andrey Yurovsky <andrey@cozybit.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mesh.h

@@ -188,8 +188,9 @@ struct mesh_rmc {
  */
 #define MESH_PREQ_MIN_INT	10
 #define MESH_DIAM_TRAVERSAL_TIME 50
-/* Paths will be refreshed if they are closer than PATH_REFRESH_TIME to their
- * expiration
+/* A path will be refreshed if it is used PATH_REFRESH_TIME milliseconds before
+ * timing out.  This way it will remain ACTIVE and no data frames will be
+ * unnecesarily held in the pending queue.
  */
 #define MESH_PATH_REFRESH_TIME			1000
 #define MESH_MIN_DISCOVERY_TIMEOUT (2 * MESH_DIAM_TRAVERSAL_TIME)

net/mac80211/mesh_hwmp.c

@@ -937,7 +937,7 @@ int mesh_nexthop_lookup(struct sk_buff *skb,
 
 	if (mpath->flags & MESH_PATH_ACTIVE) {
 		if (time_after(jiffies,
-			       mpath->exp_time +
+			       mpath->exp_time -
 			       msecs_to_jiffies(sdata->u.mesh.mshcfg.path_refresh_time)) &&
 		    !memcmp(sdata->dev->dev_addr, hdr->addr4, ETH_ALEN) &&
 		    !(mpath->flags & MESH_PATH_RESOLVING) &&