net: dsa: mv88e6xxx: Convert flag bits to unsigned long long

We are soon going to run out of flag bits on 32bit systems. Convert to
unsigned long long.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>