VCCV for static pseudowire segments

MS pseudowire is supported with a mix of static and signaled pseudowire segments. However, VCCV ping and VCCV-trace is allowed until at least one segment of the MS pseudowire is static. Users cannot test a static segment but also, cannot test contiguous signaled segments of the MS-pseudowire. VCCV ping and VCCV trace is not supported in static-to-dynamic configurations.