wil6210: enlarge TX/RX buffer length

HW supports upto 2304 packet size on the air.
HW is responsible for adding (Tx) or removing (Rx) the following headers:
802.11 hdr: 26B
SNAP: 8B
CRC: 4B
Security (optional): 24B
HW adds max 62B to the payload passed from driver. It means driver can use
max packet size of 2304-62 = 2242B

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