mac80211: move interface type to vif structure

Drivers that support mixed AP/STA operation may well need to
know the type of a virtual interface when iterating over them.
The easiest way to support that is to move the interface type
variable into the vif structure.

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