Public bug reported:

Dell systems with Type-C ports support a feature called "MAC address" pass 
through.
This feature allows systems to set a persistent system MAC address to be used 
with the TB15, WD15 and Type-C ethernet adapter.

More information is available here:
http://www.dell.com/support/article/us/en/19/SLN301147/en

This function works by a system specific MAC address (referred to as an
auxiliary mac address) being programmed in the factory.  When the driver
for the type-c ethernet (in dock or dongle) is loaded the MAC address is
supposed to be overridden with this value.

To enable this in Linux I see 3 parts of the stack that need to be fixed:
1) The value of the auxiliary address needs to be exposed to the OS in the 
kernel.
2) The "consistent driver naming scheme" needs to rename to the auxiliary name 
in a udev rule.
3) Network Mangager needs to not reset to the HW address when this scenario is 
detected.

For 1:
------
I've added support for bubbling up this information from the kernel into sysfs 
in:
/sys/devices/platform/dell-laptop/auxiliary_mac

Through this patch:
https://patchwork.kernel.org/patch/9047581/

Here is a sample of what it's output looks like:
$ cat /sys/devices/platform/dell-laptop/auxiliary_mac
847BEB5992D2

When that patch is accepted upstream, it will need to be backported to
Ubuntu to enable exporting this data.

For 2:
------
I've got a udev rule and helper script that will do this part.  I'll attach it 
to this bug.

For 3:
------
Network manager needs to know to reset the ethernet adapter to the original MAC 
address but rather to this value (if available).  As it stands today even with 
the udev rule in place if network manager is running it immediately resets:

NetworkManager[4513]: <info>  [1462846115.2330] device (en847BEB5992D2):
reset MAC address to 9C:EB:E8:30:B0:A8

squashing the udev rule.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

** Affects: network-manager (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "dell dock udev rule"
   
https://bugs.launchpad.net/bugs/1579984/+attachment/4659577/+files/75-dell-dock.rules

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https://bugs.launchpad.net/bugs/1579984

Title:
  Dell dock MAC Address pass through doesn't work in Ubuntu

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