[SCSI] libfcoe: add protocol description of FIP VN2VN mode

The FC-BB-6 committee is proposing a new FIP usage model called
VN_port to VN_port mode.  It allows VN_ports to discover each other
over a loss-free L2 Ethernet without any FCF or Fibre-channel fabric
services.  This is point-to-multipoint.  There is also a variant
of this called point-to-point which provides for making sure there
is just one pair of ports operating over the Ethernet fabric.

This patch defines the new message type and subtypes as well as
one new descriptor type used by VN2VN mode.

These are all still at the proposed stage and subject to change.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>