cfg80211: fix regression on beacon world roaming feature

cfg80211: fix regression on beacon world roaming feature

A regression was added through patch a4ed90d6:

"cfg80211: respect API on orig_flags on channel for beacon hint"

We did indeed respect _orig flags but the intention was not clearly
stated in the commit log. This patch fixes firmware issues picked
up by iwlwifi when we lift passive scan of beaconing restrictions
on channels its EEPROM has been configured to always enable.

By doing so though we also disallowed beacon hints on devices
registering their wiphy with custom world regulatory domains
enabled, this happens to be currently ath5k, ath9k and ar9170.
The passive scan and beacon restrictions on those devices would
never be lifted even if we did find a beacon and the hardware did
support such enhancements when world roaming.

Since Johannes indicates iwlwifi firmware cannot be changed to
allow beacon hinting we set up a flag now to specifically allow
drivers to disable beacon hints for devices which cannot use them.

We enable the flag on iwlwifi to disable beacon hints and by default
enable it for all other drivers. It should be noted beacon hints lift
passive scan flags and beacon restrictions when we receive a beacon from
an AP on any 5 GHz non-DFS channels, and channels 12-14 on the 2.4 GHz
band. We don't bother with channels 1-11 as those channels are allowed
world wide.

This should fix world roaming for ath5k, ath9k and ar9170, thereby
improving scan time when we receive the first beacon from any AP,
and also enabling beaconing operation (AP/IBSS/Mesh) on cards which
would otherwise not be allowed to do so. Drivers not using custom
regulatory stuff (wiphy_apply_custom_regulatory()) were not affected
by this as the orig_flags for the channels would have been cleared
upon wiphy registration.

I tested this with a world roaming ath5k card.

Cc: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>