net: dsa: loop: Support 4K VLANs

Allocate a 4K array of VLANs instead of limiting ourselves to just 5
which is arbitrary.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>