Currently port 6 is shown as up 10MBit/half in LUCI and swconfig.
Reason is that all bits in the port 6 config are zero.
This means that also the aneg flag is not set and in this case
ar8216_read_port_link hardcodes the link to be up.

This is no real problem but a little annoying.
To fix this initialize port 6 with the aneg bit enabled.
This causes ar8216_read_port_link to evaluate the link status bit which is
always zero for port 6 as no PHY is connected to this port.
And it doesn't hurt as port 6 isn't connected to anything on TL-WDR4900.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

SVN-Revision: 45749