ath9k_common: drop incomming frames with an invalid hardware rate

ath9k_common: drop incomming frames with an invalid hardware rate

ath9k_common (used by ath9k and ath9k_htc) trusts the frames
blessed by hardware as OK are infact correct even if the rate
seen by the driver is unrecognized. ath9k_common just treats
these frames in mac80211 as frames as frames under 1 mbps rate.
It seems this might not be the best thing to do as other parts of
the frame might not be valid so just drop these frames for now.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>