cfg80211: enforce disabling channels by custom or strict settings

cfg80211: enforce disabling channels by custom or strict settings

If a custom regulatory domain is passed and if a rule for a
channel indicates it should be disabled that channel should
always remain disabled as per its documentation and design.

Likewise if WIPHY_FLAG_STRICT_REGULATORY flag is set and a
regulatory_hint() is issued if a channel is disabled that
channel should remain disabled.

Without this change only drivers that set the _orig flags
appropriately on their own would ensure disallowed channels
remaind disabled. This helps drivers save code by relying on
the APIS provided to entrust channels that should not be enabled
be respected by only having to use wiphy_apply_custom_regulatory()
or regulatory_hint() with the WIPHY_FLAG_STRICT_REGULATORY set.

If wiphy_apply_custom_regulatory() is used together with
WIPHY_FLAG_STRICT_REGULATORY and a regulatory_hint() issued
later, the incoming regulatory domain can override previously
set _orig parameters from the initial custom regulatory
setting.

Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>