dpif-netdev: Don't run port names through netdev_vport_get_dpif_port().

dpif-netdev: Don't run port names through netdev_vport_get_dpif_port().

The ports that exist within a dpif have already been translated through
netdev_vport_get_dpif_port(), so there is no value to translating them
again in the interfaces that query or dump ports (and possibly a drawback
if somehow the translation could change).

After this change, dpif-netdev translates port names in just one place,
the port_add path, which makes dpif-netdev act the same way as dpif-linux
in this respect.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>