[package] base-files: utilize uci_get_state to read the previous dhcp router address...

[package] base-files: utilize uci_get_state to read the previous dhcp router address in udhcpc default script.
The setup_switch() procedure provided by swconfig calls config_load() during network restart and thus confuses
udhcpc's uci state keeping resulting in a missing default route on each second network restart. Bypass the
cached state vars and query uci directly to make the script immune against unwanted runtime changes.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@23211 3c298f89-4303-0410-b956-a3cf2f4a3e73