vhost: fix dereferencing invalid pointer after realloc

vhost: fix dereferencing invalid pointer after realloc

numa_realloc() reallocates the virtio_net device structure and
updates the vhost_devices[] table with the new pointer if the rings
are allocated different NUMA node.

Problem is that vhost_user_msg_handler() still dereferences old
pointer afterward.

This patch prevents this by fetching again the dev pointer in
vhost_devices[] after messages have been handled.

Fixes: af295ad4698c ("vhost: realloc device and queues to same numa node as vring desc")
Cc: stable@dpdk.org
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>