net/vhost: fix unix socket not removed as closing

net/vhost: fix unix socket not removed as closing

The commit aed0b12930b3 ("net/vhost: fix socket file deleted on stop")
moves rte_vhost_driver_register and rte_vhost_driver_unregister from
dev_start() and dev_stop() into driver's probe() and remove().

Apps, like testpmd, using vhost pmd in server mode, usually calls
dev_stop() and dev_close() as quitting, instead of driver-specific
remove(). Then those unix socket files have no chance to get removed.

Semantically, device-specific things should be put into device-specific
APIs. Fix this issue by moving rte_vhost_driver_unregister, plus other
structure free into dev_close().

Fixes: aed0b12930b3 ("net/vhost: fix socket file deleted on stop")
Cc: stable@dpdk.org
Reported-by: Lei Yao <lei.a.yao@intel.com>
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>