mac80211: make the beacon monitor available externally

mac80211: make the beacon monitor available externally

commit d3a910a8e4e846b9a767d35483f4dc7c6de7af82 upstream.

This will be used by other components next. The beacon
monitor was added as of 2.6.34 so these fixes are applicable
only to kernels >= 2.6.34.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>