ovn-trace: Note that no match means drop.

ovn-trace will tell you when a packet processing ends because no flow is
matched in a given logical flow table.  Update the output to clarify that
when this occurs, the packet is implicitly dropped.

The output now looks like this:

    ingress(dp="sw0", inport="sw0-port1")
    -------------------------------------
     0. ls_in_port_sec_l2: no match (implicit drop)

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>

Author: russellb

ovn/utilities/ovn-trace.c

@@ -1359,7 +1359,7 @@ trace__(const struct ovntrace_datapath *dp, struct flow *uflow,
         ds_put_format(&s, "%s, priority %d", f->match_s, f->priority);
     } else {
         char *stage_name = ovntrace_stage_name(dp, table_id, pipeline);
-        ds_put_format(&s, "%s%sno match",
+        ds_put_format(&s, "%s%sno match (implicit drop)",
                       stage_name ? stage_name : "",
                       stage_name ? ": " : "");
         free(stage_name);