[package] switch: the hardware must be up while configuring

[package] switch: the hardware must be up while configuring
Since the removal of the interface coldplug hack the timing changed in such a way that eth0 is not up during switch setup,
leading to an inaccesible device. Bring up the switch interface before configuring it to mitigate the problem.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@30937 3c298f89-4303-0410-b956-a3cf2f4a3e73