ramips: combine network setup for all boards in one file

Inspired by the patch from Roman Yeryomin. Thanks, Roman!
This removes unnecessary duplication and simplifies network setup for new
boards. It would be a one line change most likely.

[juhosg: setup lan and wan interfaces for unspecified rt3x0x based boards
in order to avoid regression]

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>

SVN-Revision: 29376