Without this port binding fails with below error:-
Network <nw> is type of vxlan but agent <host> or mechanism
driver only support ['gre', 'local', 'flat', 'vlan'].
Also fix permissions of /opt/stack/devstack in ml2 ovs testing
documentation and added these files to irrelevant-files to skip
running functional jobs as these files are not used in those jobs.
Related-Bug: #1934466
Change-Id: I3ca2ea19bf5e316e580669caab4c607447034a11