MFC r344990:
Fix ieee80211_radiotap(9) usage in wireless drivers:

- Alignment issues:
* Add missing __packed attributes + padding across all drivers; in
most places there was an assumption that pad

MFC r344990:
Fix ieee80211_radiotap(9) usage in wireless drivers:

- Alignment issues:
* Add missing __packed attributes + padding across all drivers; in
most places there was an assumption that padding will be always
minimally suitable; in few places - e.g., in urtw(4) / rtwn(4) -
padding was just missing.
* Add __aligned(8) attribute for all Rx radiotap headers since they can
contain 64-bit TSF timestamp; it cannot appear in Tx radiotap headers, so
just drop the attribute here. Refresh ieee80211_radiotap(9) man page
accordingly.

- Since net80211 automatically updates channel frequency / flags in
ieee80211_radiotap_chan_change() drop duplicate setup for these fields
in drivers.

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MFC r343990:
net80211: hide casts for 'i_seq' field offset calculation inside
ieee80211_getqos() and reuse it in various places.