net/vhost: fix invalid state

net/vhost: fix invalid state

dev_start sets *dev_attached* after setup queues, this sets device to
invalid state since no frontend is attached. Also destroy_device set
*started* to zero which makes *allow_queuing* always zero until dev_start
get called again. Actually, we should not determine queues existence by
*dev_attached* but by queues pointers or other separated variable(s).

Fixes: 30a701a53737 ("net/vhost: fix crash when creating vdev dynamically")
Cc: stable@dpdk.org
Signed-off-by: Junjie Chen <junjie.j.chen@intel.com>
Tested-by: Jens Freimann <jfreimann@redhat.com>
Reviewed-by: Jianfeng Tan <jianfeng.tan@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>