brcm80211: fmac: postpone dongle RF enabling.

BRCMF_C_UP is the command that asks the firmware to enable RF of
dongle. Some firmware initialization steps must be performed during
RF is down. Postpone BRCMF_C_UP firing until brcmf_netdev_open get
called to ensure firmware have enough time to finish
initialization.

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