ramips: add a workaround to fix failsafe on RT5350

Due to TCP connections not working when VLAN is disabled, this is
needed to get failsafe functional.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42179 3c298f89-4303-0410-b956-a3cf2f4a3e73