nl80211: ensure interface is up in various APIs

The nl80211 handling code should ensure as much as
it can that the interface is in a valid state, it
can certainly ensure the interface is running.

Not doing so can cause calls through mac80211 into
the driver that result in warnings and unspecified
behaviour in the driver.

Cc: stable@vger.kernel.org
Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>