staging: wfx: simplify handling of encrypted frames

staging: wfx: simplify handling of encrypted frames

We don't want mac80211 try to check MMIC and other security mechanisms.
So, the driver remove all the data related to the encryption (IV, ICV,
MMIC).

However, enabling RX_FLAG_PN_VALIDATED is sufficient for that.

So, drop the useless function wfx_drop_encrypt_data() and enable
RX_FLAG_PN_VALIDATED.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200701150707.222985-11-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>