cfg80211: add regulatory_hint_core() to separate the core reg hint

cfg80211: add regulatory_hint_core() to separate the core reg hint

This makes the core hint path more readable and allows for us to
later make it obvious under what circumstances we need locking or not.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>