Currently port logic is placed inconsistently: port creation is in core processing,
while port deletion is in validate_interfaces before_update. This changes moves
port creation there as well. This should only affect deployments that tamper with
validation_interfaces hook, as previously port creation was run just before running
before_update hooks.
This allows deployments to replace port creation logic by replacing the
validate_interfaces hook.
Change-Id: Idd8f748fdf31fc694bd7b554837e509024716c18
Partial-Bug: #1667472
9575d31920