vhost: handle mbuf allocation failure

vhost: handle mbuf allocation failure

vhost buffer allocation is successful for packets that fit
into a linear buffer. If it fails, vhost library is expected
to drop the current packet and skip to the next.

The patch fixes the error scenario by skipping to next packet.
Note: Drop counters are not currently supported.

Fixes: c3ff0ac70acb ("vhost: improve performance by supporting large buffer")
Cc: stable@dpdk.org
Signed-off-by: Sivaprasad Tummala <sivaprasad.tummala@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>