So the prime driver behind pinning the MTU down on our interfaces is so
traffic can cross mutlinode vxlan tunnels between nodes where the devstack
plugin is executing to support more complex tests.
But the reality is that doesn't always make sense, and when Neutron
has a default mtu override based upon "upstream" traffic constraints,
that is likey okay as well.
Part of the CI configuration auto-pins the MTU down, which is fine
for single node testing, however with multinode we need to pin the
MTU further down to try and prevent packets from being dropped on
the internal interfaces use to wire up test VMs.
Change-Id: Idc145f4eea87a8db69202b8d7953975d7d5cba2c
ec53c6b5d2