bcm53xx: try to fix network on Asus RT-AC87U

bcm53xx: try to fix network on Asus RT-AC87U

This device seems to have switch port 7 connected to the CPU:
vlan1ports=1 2 3 5 7*
vlan2ports=0 7u
it should be handled by eth1 and NVRAM seems to confirm that (no
et0macaddr entry, existing et1macaddr & et1phyaddr entries).

One of the remaining ports (4/8?) may be connected to the Quantenna SoC.
Original firmware boot log contains following messages:
(0x00,0x5d)Port 5 States Override: 0xfb
(0x00,0x5f)Port 7 States Override: 0xfb
(0x00,0x0e)Port 8 States Override: 0x0a
(why does it force port 5 state?!)

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
SVN-Revision: 45692