Mark OFP v6 port when non-optical

For OE demo port descriptions are always sent using optical port
descriptions. To differentiate non-optical ports padding between
length and hw_addr in ofp_port structure from OFP v. 5 is set to 0x0001.
Merge pull request #2 from shivarammysore/non_optical_padding

Mark OFP v6 port when non-optical