Comment 14 for bug 1878299

Reviewed: https://review.opendev.org/744186
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=b3647782e4dae56529bbf59918a51326df47b32e
Submitter: Zuul
Branch: stable/stein

commit b3647782e4dae56529bbf59918a51326df47b32e
Author: Flavio Fernandes <email address hidden>
Date: Thu Jun 25 23:34:32 2020 -0400

    port_forwarding: validate args before invoking db update

    Add validator to update_floatingip_port_forwarding so codepath does not
    attempt performing invalid database operation. With that, operation fails
    right away, with a hint on the offending argument(s).

    This is a backport that combines changes from 2 changes that go together:
    https://review.opendev.org/#/c/738145/
    https://review.opendev.org/#/c/744993/

    Note: pep8 failed with following error:
      ./neutron/tests/unit/services/portforwarding/test_pf_plugin.py:237:9:
      ./neutron/tests/unit/services/portforwarding/test_pf_plugin.py:261:9:
        N322 Possible use of no-op mock method. please use assert_called_once_with.
            mock_pf_get_objects.assert_called_once()
            ^
    So additional changes were needed for backport.

    Change-Id: I8284b22c5d691bfd9eadeb8590c3d4b27d261b04
    Closes-Bug: #1878299
    (cherry picked from commit f3797403486ba43100ff9ec8917d38c8723e12b2)
    (cherry picked from commit 838399f0a489e898cfefe49dbe026553bc117381)