ar71xx: use switchX names in network configuration

Accessing the AR8xxx switches via the name of the
attached ethernet device is not possible since
r35560. Change the uci-defaults script to use
switchX names in switch configurations.

Reported-by: Jonas Gorski <jogo@openwrt.org>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt@35561 3c298f89-4303-0410-b956-a3cf2f4a3e73