Disable DF bit for tunneled installations

[OpenStack Infra]

https://review.openstack.org/141487
commit a57c156550ebe769119df2e011a1135e8ea4598c
Author: Vladimir Kuklin <email address hidden>
Date: Fri Dec 12 23:36:49 2014 +0300

    Disable DF bit for tunneled installations

    Due to the way how OVS handles GRE tunnels
    it tries to copy DF flag to wrapping GRE
    packet header, thus making it impossible
    for packets of more than 1430 bytes size
    to be transfered through regular interfaces
    this breaks almost all applications. Thus
    we are setting dont_fragment option to false
    and we will also need to make ovs agent
    set df_inherit flag to this option for
    OVS versions that support df_inherit flag

    We will also need to document that user should
    extend his MTU size to reasonable one according
    to http://docs.openstack.org/icehouse/install-guide/install/yum/content/neutron-ml2-network-node.html
    in order to not get performance issues.

    DocImpact
    Change-Id: I031351b36f56881f21986b412bfae79fba0e884b
    Partial-bug: #1402046

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/142114
Committed: https://git.openstack.org/cgit/stackforge/fuel-docs/commit/?id=8f3cb86bec044345dd6918f0edeeb23c3bc63591
Submitter: Jenkins
Branch: master

commit 8f3cb86bec044345dd6918f0edeeb23c3bc63591
Author: Irina Povolotskaya <email address hidden>
Date: Tue Dec 16 17:17:38 2014 +0300

    Add information about MTU size

    Due to OVS behavior, we should add a note about
    setting a reasonable MTU size.

    Change-Id: Ie96a2c16b92bfb3ab488c0a2941655f07313107f
    Closes-Bug: 1402734

[Alexander Nevenchannyy (anevenchannyy)]

Verified on MOS 6.1 ISO #473
Steps to Verify:
root@node-1:~# grep -R dont_fragment /etc/neutron
/etc/neutron/plugins/ml2/ml2_conf.ini:dont_fragment=False
/etc/neutron/plugin.ini:dont_fragment=False