mac80211: remove bogus mod_timer() call

The IBSS code has a bogus mod_timer(..., 0) call,
we shouldn't ever pass a constant value to the
function since any constant value could be in the
future or the past.

However, invoking the timer here is not necessary
at all, since we just finished scanning and just
need to have the IBSS code run again from the
workqueue later, so factor out the work starting
and use that instead.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>