Description of problem, as explained by PM Marc Curry:

Our o-sdn to ovn-k migration docs state you can modify the MTU in the migration process (step 4), but it's very unclear.  I confirmed the following with engineering (Peng Liu and Zenghui Shi).

The decision process is:

• If a customer has the default MTU applied, and if they want to keep the default MTU during migration, then the optional procedure in "Step 4" of our migration product documentation can be ignored.
• If a customer has a custom MTU applied, and if they want to keep the custom MTU during migration, declare the custom MTU as described in "Step 4" of our migration product documentation.  Note: This option doesn't do anything to the host or infrastructure MTU.
• If a customer has the default MTU applied, and if they want to change the MTU during migration, then the optional procedure in "Step 4" of our migration product documentation doesn't apply.  We recommend the customer do the MTU migration first, following our documented procedure, and then do the o-sdn to ovn-k migration, separately.  When then performing the migration, use "Step 4" to keep the customized MTU (as described in the previous bulleted option). 

This issue is reported in 4.14 docs, but I assume it impacts previous versions. Please verify. Thank you!