swconfig: fix backward compatibility

swconfig: fix backward compatibility

swconfig fails to load uci configuration after the generic switch
identifier changes.

root@OpenWrt:/# uci show network | grep switch
network.@switch[0]=switch
network.@switch[0].name=eth0
network.@switch[0].reset=1
network.@switch[0].enable_vlan=1
network.@switch_vlan[0]=switch_vlan
network.@switch_vlan[0].device=eth0
network.@switch_vlan[0].vlan=1
network.@switch_vlan[0].ports=0t 2 3 4 5
network.@switch_vlan[1]=switch_vlan
network.@switch_vlan[1].device=eth0
network.@switch_vlan[1].vlan=2
network.@switch_vlan[1].ports=0t 1
root@OpenWrt:/# swconfig dev eth0 load /etc/config/network
Failed to apply configuration for switch 'switch0'
root@OpenWrt:/# swconfig dev switch0 load /etc/config/network
Failed to apply configuration for switch 'switch0'

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@27820 3c298f89-4303-0410-b956-a3cf2f4a3e73