Intel wireless 8260 - unclaimed network
Your device, Intel Corporation Wireless 8260 [8086:24f3] (rev 3a), Subsystem: Intel Corporation Device [8086:1130] is not yet covered by the driver iwlwifi. Several variations are covered, but not the exact pci.id and subsystem combination that you have. Let's try to add it.
Please download this file to your desktop: https://www.kernel.org/pub/linux/kernel/projects/backports/2015/09/23/backports-20150923.tar.gz Right-click it and select 'Extract Here.' Drill down to drivers > net > wireless > iwlwifi > pcie. Open the file drv.c with any text editor, like gedit, nano or kate. Scroll down to line 428. Please notice that your pci.id ending in 24F3 hasn't a corresponding subsystem of 1130. 24F4 has an 1130, but not your 24F3. Let's just change it. Change line 428 from:
{IWL_PCI_DEVICE(0x24F4, 0x1130, iwl8260_2ac_cfg)},
To read instead:
{IWL_PCI_DEVICE(0x24F3, 0x1130, iwl8260_2ac_cfg)},
Spacing, punctuation, brackets, etc. are crucial and must be perfect. Proofread carefully, save and close the text editor. Now:
cd ~/Desktop/backports-20150923
make clean
make defconfig-iwlwifi
make
sudo make install
Reboot. Any improvement?
You have compiled the driver for your currently installed kernel version only. When Update Manager installs a later linux-image, after the required reboot, please recompile:
cd ~/Desktop/backports-20150923
make clean
make defconfig-iwlwifi
make
sudo make install
Please retain the files and these instructions for that time.
chili555's answer was certainly correct, but I haven't tested that. I'd just like to add that support is included in updated kernels for Ubuntu 15.10. When you're installing Ubuntu, wifi won't work to get you connected, but simply use a cable to get updates. Your wifi will work after a reboot. After updates, this worked out of the box on a Thinkpad P50.
So there's no need to download, edit and compile anything any more.
To get this wireless adapter work in Ubuntu 15.10 you need to install firmware by running
wget http://mirrors.kernel.org/ubuntu/pool/main/l/linux-firmware/linux-firmware_1.156_all.deb
sudo dpkg -i linux-firmware_1.156_all.deb
For Ubuntu 14.04 you need also to upgrade the kernel by
sudo apt-get install linux-generic-lts-wily