[dts] [PATCH V4] tests/loopback_virtio_user_server_mode:modify execute virtio-user server side testpmd command after client side started

[Tu, Lijuan]

> v1:
> In DPDK 9af79db20f4cf, when launch virtio-user testpmd as server mode, virtio-
> user server side testpmd expected character will be 'wait for client side
> started...', after client side started, it change to 'testpmd>', so dts need modify
> execute virtio-user server side testpmd command after client side started.
> 
> v2:
> Fix comments about dpdk commit description error dut to checkpatch error.
> 
> v3:
> Fix comments about dpdk commit description error dut to checkpatch error.
> 
> v4:
> Fix comments about dpdk commit description error dut to checkpatch error.
> 
> Signed-off-by: Ling Wei <weix.ling at intel.com>

Applied