net/mlx5: Handle host PF vport mac/guid for ECPF

When ECPF is eswitch manager, it has the privilege to query and
configure the mac and node guid of host PF.

While vport number of host PF is 0, the vport command should be
issued with other_vport set in this case as the cmd is issued by
ECPF vport(0xfffe).

Add a specific function to query own vport mac. Low level functions
are used by vport manager to query/modify any vport mac and node guid.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>