mac80211: backport brcmfmac changes from 2016-07-08

To work correctly hostapd requires wireless driver to allow interfaces
removal. It was working with brcmfmac only partially. Firmware for
BCM43602 got some special hack (feature?) that allowed removing all
interfaces by disabling mbss mode. It wasn't working with BCM4366
firmware and remaining interfaces were preventing hostapd from starting
again.

Those patches add support for "interface_remove" firmware method which
works with BCM4366 firmware and they make it finally possible to use
BCM4366 & brcmfmac & multiple interfaces.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>