brcm80211: smac: removed down-on-rf-kill functionality

Softmac would bring its interface down on an RF kill switch condition,
without Mac80211 intervention. Because Mac80211 should be the only party
initiating interfaces going up and down, this functionality has been
removed.

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