vhost-user: drop connection on message handling failures

vhost-user: drop connection on message handling failures

There are a lot of cases where vhost-user massage handling
could fail and end up in a fully not recoverable state. For
example, allocation failures of shadow used ring and batched
copy array are not recoverable and leads to the segmentation
faults like this on the receiving/transmission path:

  Program received signal SIGSEGV, Segmentation fault.
  [Switching to Thread 0x7f913fecf0 (LWP 43625)]
  in copy_desc_to_mbuf () at /lib/librte_vhost/virtio_net.c:760
  760       batch_copy[vq->batch_copy_nb_elems].dst =

This could be easily reproduced in case of low memory or big
number of vhost-user ports.

Fix that by propagating error to the upper layer which will
end up with disconnection in case we can not report to
the message sender when the error happens.

Fixes: f689586bc060 ("vhost: shadow used ring update")
Cc: stable@dpdk.org
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>