tools/hotplug: only attempt to call 'ip route' if there is valid command

tools/hotplug: only attempt to call 'ip route' if there is valid command

The vif-route script should only call 'ip route' when 'ipcmd' has been
set, otherwise it will fail due to an incorrect command string.

This patch also adds routes for 'tap' (i.e. emulated) devices as well as
'vif' (i.e. PV) devices. Empirically offline/online commands relate to
'vif' devices, and add/remove commands relate to 'tap' devices. However,
this patch treats them equally and uses ${type_if} to distinguish. By
adding cases for add/remove the command list becomes exhaustive and hence
'ipcmd' is guaranteed to be set.

Routes for 'tap' and 'vif' devices are distinguished by a route metric.
Emulated devices are used by HVM guests until they are unplugged, at which
point the PV device becomes active. Thus 'tap' devices should get a higher
priority (i.e. lower numbered) metric than 'vif' devices.

There is also one small whitespace fix.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Acked-by: Wei Liu <wl@xen.org>
Release-acked-by: Juergen Gross <jgross@suse.com>