tools/hotplug: Fix proxy arp messing about to use correct device

tools/hotplug: Fix proxy arp messing about to use correct device

Fix an anomaly in /etc/xen/scripts/network-route.

Currently this script contains
  netdev=${netdev:-eth${vifnum}}
ie. netdev is set to eth${vifnum} by default. Unfortunately vifnum
is not set anywhere in the xen code so the default is actually the
broken "eth".  And anyway the vif number (which is what vifnum ought
to be) is not relevant.

The patch changes the default to eth0 (which is what the comment at
the top of the file says it should be).

Signed-off-by: Michael Young <m.a.young@durham.ac.uk>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>