MFC r318219:

[iwm] Properly implement iwm_wme_update callback function.

* Inspired by iwn(4) and Linux iwlwifi.

* Read wme parameters into a buffer within struct iwm_vap in
iwm_wme_update().

* If we aren't associated yet, the new settings will soon be sent
by iwm_mvm_mac_ctxt_changed() during association.

* If we are already associated, explicitly call iwm_mvm_mac_ctxt_changed()
from iwm_wme_update() to send the new settings to the firmware.

* Change iwm_mvm_ac_to_tx_fifo mapping, to fit the freebsd net80211
WME stream class numbering, instead of Linux's enum ieee80211_ac_numbers.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Import OpenBSD's iwm WiFi driver for Intel 3160/7260/7265.

There are still several bugs, but I've been using it for a while now.
Thanks to all the testers and to Adrian for his help with this
driver.

This driver isn't connected to the build yet, but it will be soon.

There's no MFC planned because the driver isn't very stable yet.

Reviewed by: adrian
Obtained from: https://github.com/rpaulo/iwm
Tested by: adrian, gjb, dumbbell (others that I forgot).
Relnotes: yes