xen-netback: switch state to InitWait at the end of netback_probe()...

...as the comment above the function states.

The switch to Initialising at the start of the function is somewhat bogus
as the toolstack will have set that initial state anyway. To behave
correctly, a backend should switch to InitWait once it has set up all
xenstore values that may be required by a initialising frontend. This
patch calls backend_switch_state() to make the transition at the
appropriate point.

NOTE: backend_switch_state() ignores errors from xenbus_switch_state()
      and so this patch removes an error path from netback_probe(). This
      means a failure to change state at this stage (in the absence of
      other failures) will leave the device instantiated. This is highly
      unlikley to happen as a failure to change state would indicate a
      failure to write to xenstore, and that will trigger other error
      paths. Also, a 'stuck' device can still be cleaned up using 'unbind'
      in any case.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>