ovn-trace: Make sure we don't exit when the port is not specified.

It might happen that the microflow doesn't have port specified or
the port is part of different datapath. In that case ovn-trace would
print warning and move to later crash on assert. Exit early instead
of crashing on assert.

Signed-off-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>

utilities/ovn-trace.c

@@ -3539,7 +3539,7 @@ trace(const char *dp_s, const char *flow_s)
     }
     uint32_t in_key = uflow.regs[MFF_LOG_INPORT - MFF_REG0];
     if (!in_key) {
-        VLOG_WARN("microflow does not specify ingress port");
+        return xstrdup("microflow does not specify ingress port");
     }
     const struct ovntrace_port *inport = ovntrace_port_find_by_key(dp, in_key);
     const char *inport_name = inport ? inport->friendly_name : "(unnamed)";