ramips: Fix network for routers without VLANs on eth0.

Some routers only have one port, so eth0 is used without VLANs for them.

Revision r47720 introduced some changes, but wrongly confused "enable" with "reset".

VLANs need to be disabled for those routers, and the switch may be reset.

Fix this, by explicitly disabling VLANs instead of resetting the switch for these routers.

Also merge duplicate configuration for the "m2m".

Signed-off-by: Vittorio Gambaletta <openwrt@vittgam.net>