BigSwitch: Create router ports synchronously

Since router ports are created as part of a
long transaction with multiple REST calls, they
need to be created sychronously. This is to prevent
the async thread from deleting them from the backend
if it can't find them in cases where they haven't been
committed to the DB yet.

Closes-Bug: #1305331
Change-Id: I2ab3c862dc6b1760199654bbd0969ac5efdbe704
Merge "BigSwitch: Create router ports synchronously"