net/mlx5e: Assign random MAC address if needed

Under SRIOV there might be a case where VFs are loaded
without pre-assigned MAC address. In this case, the VF
will randomize its own MAC.  This will address the case
of administrator not assigning MAC to the VF through
the PF OS APIs and keep udev happy.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>