ath5k: remove monitor check in receive_frame_ok filter

Monitor interfaces are never seen by the driver, so tests based on
that opmode don't make sense.  Also, we already pass all mic
failure packets.

Consequently this code is actually accepting any frames with just
crypto errors and rejecting those with CRC, FIFO, and PHY errors for
all interface types.  Adjust the code and comment accordingly.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>