This is in preparation for A-MSDU decap in A-MPDU support.
* refactor out the code to purge a single reorder slot into ampdu_rx_purge_slot().
* refactor out the code to add a frame to the given reorder slot
to ampdu_rx_add_slot().
This should be a big no-op as far as current code is concerned.
Tested:
* QCA9880v2, STA mode (11ac)
* iwn(4), STA mode (11n)
Reviewed by: avos
Differential Revision: https://reviews.freebsd.org/D10328