Simpler internal bridge for Xen on Arch using netctl

Just change 'Interface' and 'Dummy' appropriately, and you'll have a nice internal bridge for VMs without having to vswitch things. 

Description='internal bridge for xen'
Interface=in0
Dummy=dummy0
Connection=bridge
IP=no
IPCustom=("link add $Dummy type dummy"
          "link set $Dummy up"
          "link set $Dummy master $Interface")