nl80211: report 4ADDR status with GET_INTERFACE

User space tools might be interested in knowing the current
status of the 4ADDR property of an interface (when supported).

Send the status along with the other attributes when replying
to a GET_INTERFACE netlink query.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>