brcm80211: fmac: move maxctl to struct brcmf_bus

maxctl is the max size of rxctl request from protocol layer to bus
layer. Move it to bus interface structure brcmf_bus. This is part
of the fullmac bus interface refactoring.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>