For KVM version < 1.0.220, the script /etc/opt/netconfig.sh is doing:

1) add address on IFACE
2) add routes going through IFACE
3) set IFACE up

But we can't add routes to an interface which is down. So call the
script twice so that the routes are really added during the second run.

The fix for KVM can be found at nexedi/slapos@07439e2e