broadcom_sta: Add patch for supporting Linux 4.7

Patch is from Arch Linux at:

https://aur.archlinux.org/cgit/aur.git/tree/?h=broadcom-wl



I've tested building against 3.18.36, 4.4.16 and 4.7.0.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @phreedom, @vcunat