Patch 6347 removed the socket file when the interface is deleted and
when VPP process is exitting. The CLI for deleting the interface has
builtin vlib_worker_thread_barrier_sync to prevent the worker
threads from running. Unfortunately, the CLI quit does not have the
builtin vlib_worker_thread_barrier_sync. As a result, it may cause the
worker thread to crash.
The fix is to add the vlib_worker_thread_barrier_sync in vhost_user_exit.
Change-Id: I1eff81170e131098f1799662f0ab48d6fca3def7
Signed-off-by: Steven <sluong@cisco.com>
4174886436