vhost: fix double-free with zero-copy
vhost: fix double-free with zero-copy

zmbufs should be set to NULL when getting freed to avoid double free on
the same buffer pointer

Fixes: b0a985d1f340 ("vhost: add dequeue zero copy")
Cc: stable@dpdk.org

Signed-off-by: Patrick Fu <9a0e5a62d6df51dec9c1e0dc80b22878833f5aba@intel.com>
Reviewed-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>

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