vhost: improve socket layer logs

vhost: improve socket layer logs

This patch adds the Vhost socket path whenever possible in
order to make debugging possible when multiple Vhost
devices are in use. Some vhost-user layer functions are
modified to pass the device path down to the socket layer.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>