net: dsa: mv88e6xxx: Re-setup interrupts on CMODE change.

When a port changes CMODE, the SERDES interface being used can change.
Disable interrupts for the old SERDES interface, and enable interrupts
on the new.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>