nl/mac80211: allow zero plink timeout to disable STA expiration

Both wpa_supplicant and mac80211 have and inactivity timer. By default
wpa_supplicant will be timed out in 5 minutes and mac80211's it is 30
minutes. If wpa_supplicant uses a longer timer than mac80211, it will
get unexpected disconnection by mac80211.

Using 0xffffffff instead as the configured value could solve this w/o
changing the code, but due to integer overflow in the expression used
this doesn't work. The expression is:

(current jiffies) > (frame Rx jiffies + NL80211_MESHCONF_PLINK_TIMEOUT * 250)

On 32bit system, the right side would overflow and be a very small
value if NL80211_MESHCONF_PLINK_TIMEOUT is sufficiently large,
causing unexpectedly early disconnections.

Instead allow disabling the inactivity timer to avoid this situation,
by passing the (previously invalid and useless) value 0.

Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
[reword/rewrap commit log]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
index 0c8b2a7..acf441f 100644
--- a/net/mac80211/mesh.c
+++ b/net/mac80211/mesh.c
@@ -574,7 +574,8 @@
 	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
 	u32 changed;
 
-	ieee80211_sta_expire(sdata, ifmsh->mshcfg.plink_timeout * HZ);
+	if (ifmsh->mshcfg.plink_timeout > 0)
+		ieee80211_sta_expire(sdata, ifmsh->mshcfg.plink_timeout * HZ);
 	mesh_path_expire(sdata);
 
 	changed = mesh_accept_plinks_update(sdata);