ovs-dpctl, ofproto/trace: Show and handle the in_port name in flows.

With this commit, whenever the verbosity is enabled with '-m'
option, the ovs-dpctl dump-flows command will display the flows with
in_port field showing the name instead of a port number.

Conversely, one can also use a name in the in_port field with del-flow,
add-flow and mod-flow commands of ovs-dpctl. One should also be able
to use the port name when supplying the datapath flow as an input
to ofproto/trace command.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>