vhost: prefetch available ring
vhost: prefetch available ring

Signed-off-by: Yuanhan Liu <5dcef21195e64c9c08aa779bb62b25e9133eaa33@linux.intel.com>
Signed-off-by: Zhihong Wang <efad9c89b3a8db7900a2572fdee08ebbff3cfc6b@intel.com>
Reviewed-by: Jianbo Liu <ad48e27d4475ec2c10ba93ba465af79f05639344@linaro.org>
Tested-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk