NetworkMonitor.get_default() hangs consuming 100% of a core, blocking unattended-upgrades

[Clint Armstrong]

On an Ubuntu Server operating as a BGP router with over 800k routes, the call to NetworkMonitor.get_default() invoked by unattended-upgrades will hang indefinitely consuming a cpu core.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: python3-gi 3.20.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-72.81~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-72-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.21
Architecture: amd64
Date: Thu Jan 9 16:03:20 2020
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm-kitty
 PATH=(custom, no user)
 LANG=en_US
 LANGUAGE=en_US:
SourcePackage: pygobject
UpgradeStatus: No upgrade log present (probably fresh install)