ovs-port: rename {attach,detach}_port() to {attach,detach}_iface()

The use of "port" term in the conscious language fix, commit bcc958c4 ('device: rename {enslave,release}_slave() to {attach,detach}_port()'), clashes with the use of the term in OVS lingo.

More specifically, "port" is used as a generic term for a device that's subordinate relationship with another. In OpenVSwitch, though, "port" means a device that "interface" devices are subordinate to.

Trying to use the both meanings at the same time makes the code supremely difficult to follow. Let's stick with the OpenVSwitch terms whenever possible.

This mostly involves change from (device <- port), to (port <- iface).