Fix TypeError for port_binding
Fix TypeError for port_binding

The function get_binding_levels can return None if the binding
host is None. But the patch [1] did not handle such case. When
the code hit the max retry limit, it will raise a TypeError.
This patch adds a data check condition before the loop.

[1] https://review.opendev.org/c/openstack/neutron/+/606827

Closes-Bug: #1906381
Change-Id: Ifd68bf3f6bd61ae8f38e9e92d736f62f4f4f48cc

openstack/neutron,openstack/neutron,mahak/neutron,mahak/neutron,openstack/neutron,mahak/neutron