conntrack-sync: T4237: Fix checks for listen-address list to str

[sever-sever]

Change Summary

Verify section conntrack_sync.py function 'is_addr_assigned'
should checks address as a string, not as a list

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4237

Component(s) name

conntrack-sync

Proposed changes

How to test

Expected commit without errors

set interfaces ethernet eth0 address '192.168.0.50/24'
set high-availability vrrp group FOO interface 'eth0'
set high-availability vrrp group FOO virtual-address '192.168.0.254/24'
set high-availability vrrp group FOO vrid '10'
set high-availability vrrp sync-group SG member 'FOO'
set service conntrack-sync failover-mechanism vrrp sync-group 'SG'
set service conntrack-sync interface eth0
set service conntrack-sync listen-address '192.168.0.50'

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly