wlantest: Support HT Control field in QoS Data frames

wlantest: Support HT Control field in QoS Data frames

Extend Data frame processing (and decryption) to handle +HTC frames by
skipping the HT Control field at the end of the frame header. While this
is not an exact match of the rules in IEEE Std 802.11-2020 for when the
HT Control field is present in frames (e.g., no check of the TXVECTOR
value), this is good enough to cover the most likely used cases.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>