Register and implement the TDLS cfg80211 callback functions.

Internally prepare and send TDLS management frames. We incorporate
local STA capabilities and supported rates with extra IEs given by
usermode. The resulting packet is either encapsulated in a data frame,
or assembled as an action frame. It is transmitted either directly or
through the AP, as mandated by the TDLS specification.

Declare support for the TDLS external setup wiphy capability. This
tells usermode to handle link setup and discovery on its own, and use the
kernel driver for sending TDLS mgmt packets.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Cc: Kalyan C Gaddam <chakkal@iit.edu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>