spapr: implement H_CHANGE_LOGICAL_LAN_MAC h_call

Since kernel v4.0, linux uses H_CHANGE_LOGICAL_LAN_MAC to change lively
the MAC address of an ibmveth interface.

As QEMU doesn't implement this h_call, we can't change anymore the
MAC address of an spapr-vlan interface.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>