Since we enqueued the frame that was supposed to be sent
during the SP, and that frame may very well cary the
IEEE80211_TX_STATUS_EOSP bit, we may never close the SP
(WLAN_STA_SP will never be cleared). If that happens, we
will not open any new SP and will never respond to any poll
frame from the client.
Clear WLAN_STA_SP manually if a frame that was polled during
the SP is queued because of a starting A-MPDU session. The
client may not see the EOSP bit, but it will at least be
able to poll new frames in another SP.

Reported-by: Alesya Shapira <alesya.shapira@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
[remove erroneous comment]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>