mac80211: allow changing port control protocol

Some vendor specified mechanisms for 802.1X-style
functionality use a different protocol than EAP
(even if EAP is vendor-extensible). Support this
in mac80211 via the cfg80211 API for it.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>