Description

Steps to reproduce the issue

Create PR at sonic-buildimage to update sonic-utilities submodule pointer to include the following:
784a15c [vlan] Refresh dhcpv6_relay config while adding/deleting a vlan (#2660)

Describe the results you received

Cannot pass check

Describe the results you expected

Update success

Additional information you deem important (e.g. issue happens only occasionally)

Caused by inconsistency between the config_db and yang model. Introduced by this PR: #2660

Output of show version

(paste your output here)