mac80211: add helper for reseting the connection monitor

This will be used in another place later. The connection
monitor was added as of 2.6.35 so these fixes will be
applicable to >= 2.6.35.

Cc: stable@kernel.org
Cc: Paul Stewart <pstew@google.com>
Cc: Amod Bodas <amod.bodas@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>