carl9170: fix AMPDU TX_CTL_REQ_TX_STATUS handling

Previously the driver did not care if TX_CTL_REQ_TX_STATUS
was set on aggregated frames or not and it would silently
drop successfully sent frames if possible [much like:
"no news is good news!"].

But, TX_CTL_REQ_TX_STATUS was invented for a reason and
no tx status report should ever be dropped if it is set.

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