MAC Spoofing is broken in Stretch

Originally created by @anonym on #11931 (Redmine)

The automated test suite noticed that the even though MAC spoofing is enabled and reportedly succeeds, the MAC address is not spoofed. I see this in the journal:

Nov 16 00:00:31 amnesia spoof-mac[2654]: Trying to spoof MAC address of NIC eth0...
[...]
Nov 16 00:00:31 amnesia spoof-mac[2719]: Successfully spoofed MAC address of NIC eth0

However:

$ macchanger eth0
Current MAC:   52:54:00:d7:d3:0f (unknown)
Permanent MAC: 52:54:00:d7:d3:0f (unknown)

Feature Branch: bugfix/11931-network-manager-vs-mac-spoofing

Related issues

• Related to #11293
• Blocked by #11937 (closed)