Currently, a function misnamed ieee80211_init_client() is used to handle
regulatory domain control. It is called from
ieee80211_register_hwmode(), which typically runs 2 or 3 times
(802.11a/b/g), but each time it iterates over all the modes.

This patch cleans this up and removes the confusion:
ieee80211_init_client was effectively renamed to
ieee80211_set_default_regdomain and is now run on a per-mode basis
(doesn't have to deal with netdevs). I also moved the regdomain handling
code into its own file and added some documentation.

Signed-off-by: Daniel Drake <dsd@gentoo.org>
Acked-by: Jiri Benc <jbenc@suse.cz>
Signed-off-by: John W. Linville <linville@tuxdriver.com>