net/ncsi: make one oem_gma function for all mfr id

Make the one Get Mac Address function for all manufacturers and change
this call in handlers accordingly.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Ivan Mikhaylov <fr0st61te@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>