Cortina phy does not have kernel driver and we don't attach
device with phy layer for intefaces like XFI, XLAUI etc,
Hence check for interface type before calling disconnect.

Signed-off-by: Thanneeru Srinivasulu <tsrinivasulu@caviumnetworks.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>