brcmfmac: use fwil for netdev callbacks.

Change setting up multicast, mac address and offloading to use the
refactored firmware interface layer. Remove obsolete brcmf_proto_dcmd
function.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>