ofproto: Add support for OF1.3 port description multipart message.

ofproto: Add support for OF1.3 port description multipart message.

OpenFlow 1.0 is limited to displaying 1364 ports in the Features Reply
message, and there is no other way to get consolidated port information.
OpenFlow 1.3 adds a new port description multipart message
(OFPMP_PORT_DESC) that is not limited by size.  This commit adds support
through the OpenFlow 1.0 stats mechanism, since they have complimentary
enum values.

Bug #11040

Signed-off-by: Justin Pettit <jpettit@nicira.com>