Comment 7 for bug 1702685

Based on advice by jeremy31 at Ubuntu Forums in https://ubuntuforums.org/showthread.php?t=2364875, I ran "dkms status" and got
09:38 AM ~ $ dkms status
ath9k-msi, 1.0, 4.4.0-81-generic, x86_64: installed
ath9k-msi, 1.0, 4.4.0-83-generic, x86_64: installed
intel-hid, 3.1, 4.4.0-81-generic, x86_64: installed
intel-hid, 3.1, 4.4.0-83-generic, x86_64: installed
oem-audio-hda-daily, 0.201612080732~ubuntu16.04.1, 4.4.0-81-generic, x86_64: installed
radeon-si, 1a, 4.4.0-38-generic, x86_64: built
radeon-si, 1a, 4.4.0-81-generic, x86_64: installed
radeon-si, 1a, 4.4.0-83-generic, x86_64: installed
09:41 AM ~ $

I then ran "sudo dkms remove -m ath9k-msi -v 1.0 -k 4.4.0-83-generic" with the following output:
09:41 AM ~ $ sudo dkms remove -m ath9k-msi -v 1.0 -k 4.4.0-83-generic

-------- Uninstall Beginning --------
Module: ath9k-msi
Version: 1.0
Kernel: 4.4.0-83-generic (x86_64)
-------------------------------------

Status: Before uninstall, this module version was ACTIVE on this kernel.

ath.ko:
 - Uninstallation
   - Deleting from: /lib/modules/4.4.0-83-generic/updates/dkms/
 - Original module
   - No original module was found for this module on this kernel.
   - Use the dkms install command to reinstall any previous module version.

ath9k.ko:
 - Uninstallation
   - Deleting from: /lib/modules/4.4.0-83-generic/updates/dkms/
 - Original module
   - No original module was found for this module on this kernel.
   - Use the dkms install command to reinstall any previous module version.

ath9k_common.ko:
 - Uninstallation
   - Deleting from: /lib/modules/4.4.0-83-generic/updates/dkms/
 - Original module
   - No original module was found for this module on this kernel.
   - Use the dkms install command to reinstall any previous module version.

ath9k_htc.ko:
 - Uninstallation
   - Deleting from: /lib/modules/4.4.0-83-generic/updates/dkms/
 - Original module
   - No original module was found for this module on this kernel.
   - Use the dkms install command to reinstall any previous module version.

ath9k_hw.ko:
 - Uninstallation
   - Deleting from: /lib/modules/4.4.0-83-generic/updates/dkms/
 - Original module
   - No original module was found for this module on this kernel.
   - Use the dkms install command to reinstall any previous module version.

depmod.........

Backing up initrd.img-4.4.0-83-generic to /boot/initrd.img-4.4.0-83-generic.old-dkms
Making new initrd.img-4.4.0-83-generic
(If next boot fails, revert to initrd.img-4.4.0-83-generic.old-dkms image)
update-initramfs...............

DKMS: uninstall completed.
09:43 AM ~ $

On rebooting and choosing the 4.4.0-83 kernel, wifi is working "out of the box".