vswitchd: show DPDK version

Show DPDK version if Open vSwitch is compiled with DPDK support.
Version can be retrieved with `ovs-vswitchd --version` or from OVS logs.
Small change in ovs-ctl to avoid breakage on output change.

Signed-off-by: Matteo Croce <mcroce@redhat.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/dpdk-stub.c

@@ -54,3 +54,8 @@ dpdk_vhost_iommu_enabled(void)
 {
     return false;
 }
+
+void
+print_dpdk_version(void)
+{
+}