Modify docstring on send_delete_port_request in N1kv plugin

N1kv plugin: Modify docstring on _send_delete_port_request method

Change-Id: I64d34878ffd8f6db703e4c1d9849032fef9bae96
Closes-Bug: #1381277
Merge "Modify docstring on send_delete_port_request in N1kv plugin"