(split) Try to make sure the frame is indeed in the kernel memory.
(split) Fix the RT2860_TX_SW_CFG2 init value on older revisions of RT3070 chip.
(split) The r48589 promised to remove implicit inclusion of if_var.h soon. Prepare
to this event, adding if_var.h to files that do need it. Also, include
all includes that now are included due to implicit pollution via if_var.h

Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
(split) Merge branch 'CURRENT' (commit 'dc6ffa39')