ifconfig: T6972: smoketests fail as IP address is not removed in time

[c-po]

Change Summary

From time to time integration tests fail as the DHCP assigned IP address is not removed in time then dhclient stops. Add an explicit code path cleaning dynamic assigned addresses from interface when disabling DHCP - if such a dynamic address is remaining.

====================================================================== FAIL: test_dhcp_vrf (__main__.EthernetInterfaceTest.test_dhcp_vrf) ---------------------------------------------------------------------- Traceback (most recent call last):
  File "/usr/libexec/vyos/tests/smoke/cli/test_interfaces_ethernet.py", line 72, in tearDown
    self.assertNotIn(AF_INET, ifaddresses(interface))
AssertionError: 2 unexpectedly found in {17: [{'addr': '52:54:00:00:00:00',
  'broadcast': 'ff:ff:ff:ff:ff:ff'}], 2: [{'addr': '192.0.2.103', 'netmask': '255.255.255.0',
  'broadcast': '192.0.2.255'}], 10: [{'addr': 'fe80::5054:ff:fe00:0%eth0',
  'netmask': 'ffff:ffff:ffff:ffff::/64'}]}

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://vyos.dev/T6972

Related PR(s)

Component(s) name

DHCP client

Smoketest result

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

[github-actions]

👍
No issues in PR Title / Commit Title

[github-actions]

CI integration ❌ failed!

Details

CI logs

• CLI Smoketests (no interfaces) ❌ failed
• CLI Smoketests (interfaces only) 👍 passed
• Config tests 👍 passed
• RAID1 tests 👍 passed
• TPM tests 👍 passed