ovn-trace: Fix tracing when ip.dst has to go via a gateway router

ovn-trace does not trace past an l3gateway port type. This patch
fixes it.

Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=1626080
Suggested-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Mark Michelson <mmichels@redhat.com>

ovn/utilities/ovn-trace.c

@@ -645,6 +645,15 @@ read_ports(void)
         } else if (!strcmp(sbpb->type, "l3gateway")) {
             /* Treat all gateways as local for our purposes. */
             dp->has_local_l3gateway = true;
+            const char *peer_name = smap_get(&sbpb->options, "peer");
+            if (peer_name) {
+                struct ovntrace_port *peer
+                    = shash_find_data(&ports, peer_name);
+                if (peer) {
+                    port->peer = peer;
+                    port->peer->peer = port;
+                }
+            }
         }
     }