ovs-dpctl: New --names option to use port names in flow dumps.

ovs-dpctl: New --names option to use port names in flow dumps.

Until now, printing names in "ovs-dpctl dump-flows" was tied to the overall
output verbosity, which in practice meant that to see port names a user had
to see a distracting amount of verbosity.  This decouples names from
verbosity.

I'd like to make showing names the default for interactive usage, but so
far names aren't accepted in input so that would frustrate cut-and-paste,
which is an important use of "ovs-dpctl dump-flows" output.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Jan Scheurich <jan.scheurich@ericsson.com>
Tested-by: Jan Scheurich <jan.scheurich@ericsson.com>