ath10k: fix shared WEP

When static keys are used in shared WEP, when a
station is associated, message 3 is sent with an
encrypted payload. But, for subsequent
authentications that are triggered without a
deauth, the auth frame is decrypted by the HW.

To handle this, check if the WEP keys have already
been set for the peer and if so, mark the
frame as decrypted. This scenario can happen
when a station changes its default TX key and initiates
a new authentication sequence.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>