libipw: initiate cfg80211 API conversion (v2)

Initiate the conversion of libipw to the new cfg80211 configuration API.

For now, leave CONFIG_IPW2200_PROMISCUOUS stuff alone.  Eventually
migrate it to cfg80211 when the add/del/change_virtual_intf methods
are implemented.

(v2: Fix unconditional wiphy_unregister in libipw which was causing
     problems for ipw2100, somewhat based on prior attempted fix
     by Zhu Yi <yi.zhu@intel.com>.  Previously both original version of
     this patch and Zhu Yi's fix attempt were reverted due to
     discovery of regressions. -- JWL)

Signed-off-by: John W. Linville <linville@tuxdriver.com>