mac80211: add hardware restart function

Some hardware defects may require the hardware to be re-initialised
completely from scratch. Drivers would need much information (for
instance the current MAC address, crypto keys, beaconing information,
etc.) stored duplicated from mac80211 to be able to do this, so let
mac80211 help them.

The new ieee80211_restart_hw() function requires the same code as
resuming, so move that code into a new ieee80211_reconfig() function
in util.c and leave only the suspend code in pm.c.

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