Drop and recreate FK if adding new PK to routerl3bindings

Since MySQL 5.6 FK columns cannot be altered. As a workaround we can
drop the FK before ALTER COLUMN and then recreate it.

Change-Id: Icd1b3075cf29a6b0c477a4ddea2e6ebee91baef8
Closes-Bug: 1384555
(cherry picked from commit b5f1cc48b877caaebc944154d56a8bb4060aa9b0)
Merge "Drop and recreate FK if adding new PK to routerl3bindings" into stable/juno