[infiniband] Add node GUID as distinct from the first port GUID

[infiniband] Add node GUID as distinct from the first port GUID

iPXE currently uses the first port's port GUID as the node GUID,
rather than using the (possibly distinct) real node GUID.  This can
confuse opensm during the handover to a loaded OS: it thinks the port
already belongs to a different node and so discards our port
information with a warning message about duplicate ports.  Everything
is picked up correctly on the second subnet sweep, after opensm has
established that the "old" node no longer exists, but this can delay
link-up unnecessarily by several seconds.

Fix by using the real node GUID.

Signed-off-by: Michael Brown <mcb30@ipxe.org>