mac80211: convert master interface to netdev_ops

Also call our own ieee80211_master_setup routine instead of
overwriting almost all the values from ether_setup; this
loses a few assignments that are pointless on the master
interface anyway.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>