staging: wfx: fix possible panic with re-queued frames

staging: wfx: fix possible panic with re-queued frames

When the firmware rejects a frame (because station become asleep or
disconnected), the frame is re-queued in mac80211. However, the
re-queued frame was 8 bytes longer than the original one (the size of
the ICV for the encryption). So, when mac80211 try to send this frame
again, it is a little bigger than expected.
If the frame is re-queued secveral time it end with a skb_over_panic
because the skb buffer is not large enough.

Note it only happens when device acts as an AP and encryption is
enabled.

This patch more or less reverts the commit 049fde130419 ("staging: wfx:
drop useless field from struct wfx_tx_priv").

Fixes: 049fde130419 ("staging: wfx: drop useless field from struct wfx_tx_priv")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20210208135254.399964-1-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>