mwifiex: update statistics for bridged packets on AP interface

The bridged packets are updated to statistics on both TX and RX
paths. Also fix a typo in the comment.

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>