[PATCH] zd1211rw: Don't handle broken frames in monitor mode

Using monitor mode, Johannes Berg observed out that lots of corrupted
and otherwise invalid frames were being passed to the host.

When in monitor mode we were disabling the hardware filtering here, but
this is not how monitor mode should work.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>