b53: Allow using all ports on BCM53012

This chipset has at least 8 usable ports, e.g. Netgear R8000 has ports
5, 7 and 8 connected to Ethernet interfaces:
vlan1ports=0 1 2 3 5 7 8*
vlan2ports=4 8u
Port 6 seems to be always disabled.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Jonas Gorski <jogo@openwrt.org>

SVN-Revision: 45676