TrivialFix: Fix help messages for port set
TrivialFix: Fix help messages for port set

Certain messages in ``port set`` were incorrect as mentioned
in [1] which are fixed in this patch.

[1]:https://review.openstack.org/#/c/300309/6/doc/source/command-objects/port.rst
TrivialFix

Change-Id: Icb8e91664fea590cd4202f80d61a82eb50b22403

dtroyer/python-openstackclient,openstack/python-openstackclient,redhat-openstack/python-openstackclient,redhat-openstack/python-openstackclient,dtroyer/python-openstackclient,openstack/python-openstackclient