net-timestamp: no-payload option in txtimestamp test

Demonstrate how SOF_TIMESTAMPING_OPT_TSONLY can be used and
test the implementation.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc Documentation/networking/timestamping/txtimestamp.c
Simple merge