[fcoe] Request SPMA iff FIP advertisement indicates support for SPMA

[fcoe] Request SPMA iff FIP advertisement indicates support for SPMA

We currently set both the FP and SP bits in our FIP FLOGI, to allow
the FCF the choice of selecting either a fabric-provided or a server-
provided MAC address.  This complies with the FCoE specification, but
has been observed to result in an FLOGI rejection from some FCFs.

Fix by recording whether or not the FCF supports SPMA, and requesting
only one of FPMA or SPMA in our FIP FLOGI.  We choose to prefer SPMA
where available, because many iPXE drivers will not be able to receive
unicast packets sent to a non-default MAC address.

Reported-by: Hadar Hen Zion <hadarh@mellanox.co.il>
Signed-off-by: Michael Brown <mcb30@ipxe.org>