Don't emit ICMP need to frag on LRP with no IPv4 address

Prior to this patch, when a LRP has only IPv6 addresses, ovn-northd
will crash (SIGSEV) because the current code injects a flow to
emit the ICMP need-to-frag from its IPv4 address which does not
exist.

This patch is adding a check to skip the flow installation in case
the port does not have any IPv4 address.

Signed-off-by: Daniel Alvarez <dalvarez@redhat.com>
Acked-By: Lucas Alvares Gomes <lucasagomes@gmail.com>
Acked-by: Mark Michelson <mmichels@redhat.com>
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>

northd/ovn-northd.c

@@ -7705,7 +7705,8 @@ build_lrouter_flows(struct hmap *datapaths, struct hmap *ports,
             for (size_t i = 0; i < od->nbr->n_ports; i++) {
                 struct ovn_port *rp = ovn_port_find(ports,
                                                     od->nbr->ports[i]->name);
-                if (!rp || rp == od->l3dgw_port) {
+                if (!rp || rp == od->l3dgw_port ||
+                    !rp->lrp_networks.ipv4_addrs) {
                     continue;
                 }
                 ds_clear(&match);