Don't require sed to support the -r option.

Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>

tools/examples/network-bridge

@@ -59,7 +59,7 @@ dir=$(dirname "$0")
 findCommand "$@"
 evalVariables "$@"
 
-vifnum=${vifnum:-$(ip route list | awk '/^default / { print $NF }' | sed -r 's/[^0-9]+//')}
+vifnum=${vifnum:-$(ip route list | awk '/^default / { print $NF }' | sed 's/^[^0-9]*//')}
 bridge=${bridge:-xenbr${vifnum}}
 netdev=${netdev:-eth${vifnum}}
 antispoof=${antispoof:-no}