rtl8187: Fix for TX sequence number problem

"mac80211: fix TX sequence numbers" broke rtl8187. This
patch makes the same kind of fix that was done for rt2x00. Note that
this code will have to be reworked for proper sequence numbers on beacons.
In addition, the sequence number has been placed in the hardware state,
not the vif state.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>