vhost_vring_call() used rte_mb(), which translates into
mfence instruction on x86.
This patch changes to use rte_smp_mb(), which changed recently
to translate into a locked ADD instruction for performance
reason.
The measured gain is up to 3% with the testpmd benchmarks.
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>