addons: bridge: fix default pvid handling in cases where cache is stale

addons: bridge: fix default pvid handling in cases where cache is stale

Ticket: CM-12355
Reviewed By: julien, nikhil
Testing Done: tested with failing config

This can happen if the bridge vlans were
cached before the interface become a bridge port.
and when the interface becomes a bridge port
kernel adds a default pvid of 1. so this patch
assumes a default pvid is 1 if we did not find
anything in the cache. This will delete
the default pvid of 1 if the user has configured a
different pvid.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>