LinuxKPI: 802.11: hardware crypto offload improvements

Implement mac80211 functions ieee80211_iter_keys[_rcu](), and
ieee80211_get_key_rx_seq() (*).
Implement an internal function lkpi_sta_del_keys() to delete keys
when we are leaving RUN (AUTHORIZED) state.
Improve and make work (*) the net80211 vap function pointers
(*iv_key_set)(), (*iv_key_delete)() implementations.
Correct the logic in lkpi_80211_txq_tx_one() and factor most crypto
related bits out into lkpi_hw_crypto_prepare() (*).

(*) We are currently supporting CCMP only. I would hope we will
not have to do full WEP/TKIP support anymore given both are deprecated.

The entire logic remains behind the LKPI_80211_HW_CRYPTO pre-processor
condition and with this commit in addition behind a tunable.
The code is compiled in by default now but the tunable remains off until
wider testing has shown no problems.
I have seen one net80211 triggered panic on shutdown related to deleting
keys which I cannot reproduce anymore and could have been fixed by
9763fec11b83; otherwise we will have to investigate as it shows again.
The dedicated hw crypto tracing option can help in that case with debug
kernels.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Fixes: b35f6cd06612