ath6kl: send TCMD response through testmode events

ath6kl no longer knows what it is transmitting through
cfg80211_testmode, and simply passes opaque buffers between userspace
and the firmware. Leave the CONT_RX enum for backwards compatibility.

kvalo: change ATH6KL_TM_CMD_RX_REPORT to return -EOPNOTSUPP

Signed-off-by: Thomas Pedersen <twpedersen@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>