mac80211: mesh_plink: don't ignore holding timer

The ignore_plink_timer flag is set when doing mod_timer() if
the timer was not previously active.  This is to avoid executing
the timeout if del_timer() was subsequently called.  However,
del_timer() only happens if we are moving to ESTAB state or
get a close frame while in HOLDING.

We cannot leave HOLDING and re-enter ESTAB unless we receive a
close frame (in which case ignore_plink_timer is already set) or
if the timeout expires, so there actually isn't a case where
this is needed on mod_timer().

Signed-off-by: Bob Copeland <bob@cozybit.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>