rt2x00: Fix stuck queue in tx failure case

Since commit 0b7fde54 "rt2x00: Protect
queue control with mutex" rt2x00 used rt2x00queue_pause_queue for
stopping a tx queue in mac80211. But in case of a failure in the tx
path rt2x00 still called ieee80211_stop_queue which stopped the queue
but prevented rt2x00queue_unpause_queue to wake the queue up again
resulting in a stuck tx queue.

Fix this by also using rt2x00queue_pause_queue in case of tx failures.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>