brcm80211: smac: enable/disable radio on regulatory updates

Currently the radio disable state is only updated during initialization,
and it's only checked against the internal world domain. This is
unnecessary, as there are always valid channels against this domain.
Instead, check whether any channels are enabled in the regulatory
notifier and update the radio state accordingly.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>