Reduce neutron configuration as follows:
1) Limit [ml2*] sections to neutron server containers [1].
2) Remove the [vlan] section everywhere because it only
pertains to the defunct Linux bridge monolithic
plug-in [2].
3) Explicitly disable VXLAN if deployment only includes flat
or VLAN networks [3].
4) Limit Linux bridge agent configuration options to neutron
agent containers.
5) Remove [agent] tunnel_type option because the Linux bridge
agent does not use it.
6) Move some options to correct locations.
7) Reorder some options to improve readability.
8) Annotate groups of options or specific options.
[1] https://review.openstack.org/#/c/196759/
[2] https://review.openstack.org/#/c/196765/
[3] https://review.openstack.org/#/c/160826/
Change-Id: I275fb600360530534f7673e6eb2a3d397b10fb8e
Closes-Bug: #1473230
4f4d81acb5