brcmfmac: support critical protocol API for DHCP

Adds support for the critical protocol API provided by nl80211
which gives Wifi traffic priority over a Bluetooth (e)SCO connection
and disables scanning during DCHP negotiation.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Piotr Haber <phaber@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>