[hermon] Use Ethernet MAC as eIPoIB local EMAC

[hermon] Use Ethernet MAC as eIPoIB local EMAC

The eIPoIB local Ethernet MAC is currently constructed from the port
GUID.  Given a base GUID/MAC value of N, Mellanox seems to populate:

  Node GUID:   N + 0
  Port 1 GUID: N + 1
  Port 2 GUID: N + 2

and

  Port 1 MAC:  N + 0
  Port 2 MAC:  N + 1

This causes a duplicate local MAC address when port 1 is configured as
Infiniband and port 2 as Ethernet, since both will derive their MAC
address as (N + 1).

Fix by using the port's Ethernet MAC as the eIPoIB local EMAC.  This
is a behavioural change that could potentially break configurations
that rely on the local EMAC value, such as a DHCP server relying on
the chaddr field for DHCP reservations.

Signed-off-by: Christian Iversen <ci@iversenit.dk>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>