dpdk: Deprecate vhost-user server ports.

dpdk: Deprecate vhost-user server ports.

Since vhost-user server mode ports are the preferred mechanism for
interconnecting Open vSwitch with VMs when using DPDK, and since there
are currently no known use cases for vhost-user server mode ports apart
from version incompatibilities with QEMU, announce that server mode ports
are considered deprecated and will be removed in a future release.

Cc: Ciara Loftus <ciara.loftus@intel.com>
Cc: Kevin Traynor <ktraynor@redhat.com>
Suggested-by: Darrell Ball <dball@vmware.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Darrell Ball <dlu998@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>