ath25: fix preinit Ethernet port configuration

ath25: fix preinit Ethernet port configuration

vconfig is no more installed by default to a firmware image. So, replace
vconfig calls for VLAN subinterface configuration by coresponding
ip-link commands.

Also drop few useless comments from the preinit hook script, while we
are at it.

I have no chance to test this fix since I have no board with a subject
switch IC, but this is still better then call an utility that is
unavailable in the firmware for years.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
[use documented syntax for ip link add]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>