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

Author: reedip

doc/source/command-objects/port.rst

@@ -135,9 +135,9 @@ Set port properties
 
 .. option:: --fixed-ip subnet=<subnet>,ip-address=<ip-address>
 
-    Desired IP and/or subnet for this port:
+    Desired IP and/or subnet (name or ID) for this port:
     subnet=<subnet>,ip-address=<ip-address>
-    (you can repeat this option)
+    (this option can be repeated)
 
 .. option:: --no-fixed-ip