wil6210: Tx mgmt frame from debugfs

wil6210: Tx mgmt frame from debugfs

Provide 2 files on the debugfs:
- "rxon": write channel (1..4) to open Rx on it, 0 to rxoff
- "tx_mgmt": write binary frame, starting from MAC header

one need to care about turning receiver on/off before/after tx_mgmt

Correct sequence is:
 echo $channel > rxon
 cat mfmt_frame > tx_mgmt
 echo 0 > rxon

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>