My commits:
https://github.com/Dmitry-Eremeev/NetworkManager/commit/a3e36a4c2f3e8b7332cdd76da0309b0ffeef2621

Environment
--------------
RHEL 8.0
NetworkManager 1.14.0
installed vrouter.ko for running kernel version (unloaded)
installed vif utility (contrail-vrouter-utils)

How to build RPMs
------------------
git clone --single-branch --branch contrail-vrouter https://github.com/progmaticlab/NetworkManager.git
export PYTHON=python3
export NM_RPMBUILD_ARGS="--without=adsl --without=bluetooth --without=wwan --without=team --without=wifi --without=ovs"
NetworkManager/contrib/fedora/REQUIRED_PACKAGES
NetworkManager/contrib/fedora/rpm/build.sh

How to apply Contrail vrouter plugin
------------------
dnf remove -y NetworkManager-libnm*
rpm -iv NetworkManager/contrib/fedora/rpm/latest/RPMS/x86_64/NetworkManager-libnm
rpm -iv NetworkManager/contrib/fedora/rpm/latest/RPMS/x86_64/NetworkManager-1.14.0*
rpm -iv NetworkManager/contrib/fedora/rpm/latest/RPMS/x86_64/NetworkManager-contrail-1.14*
systemctl daemon-reload
systemctl restart NetworkManager

Usage
-------
nmcli c add type contrail-vrouter physdev enp0s3 conn.interface vhost0 autoconnect no
nmcli c up contrail-vrouter-vhost0
nmcli c down contrail-vrouter-vhost0

Troubleshooting
----------------
To set maximum log level:
nmcli general logging level TRACE domains ALL

To get all system logs regarding the component "NetworkManager" for last hour and get new logs in real time (tail -f):
journalctl -f --no-tail --since "1 hour ago" -u NetworkManager

To get all system logs regarding the component "NetworkManager" with keyword "CONTRAILl" for last hour and get new logs in real time (tail -f):
journalctl -f --no-tail -g "CONTRAIL" --since "1 hour ago" -u NetworkManager

To load vrouter module or get error message if it's already loaded:
modprobe -v --first-time vrouter

To unload vrouter module or get error message if it's already unloaded:
modprobe -rv --first-time vrouter

To get log level for core component of NetworkManager:
nmcli general logging

To get list of network devices (network interfaces):
nmcli device

To set debug log level for core component of NetworkManager:
nmcli g log level DEBUG

To notify NetworkManager about changes after connection profile was manually changed (/etc/NetworkManager/system-connections/), not by nmcli means
nmcli connection reload

To delete all connection profiles with keyword "vhost" in their names (by means of nmcli):
for i in `nmcli -f NAME c show | grep "vhost"`; do nmcli c del $i; done

To delete all connection profiles with keyword "contrail" in their names (manual deleting, not by nmcli means):
rm -rf /etc/NetworkManager/system-connections/contrail*