Description of problem:

Changes were introduced in 4.12 which allowed the designated router (DR) IP to be something other than the .3 address in the per node pod subnet. However, downstream ICNIv1 code was not updated. Therefore the DR may have an IP other than .3, while an ICNIv1 pod has a default route pointing to .3. This results in no egress traffic working from the pod.

Example pod in ICNIv1 namespace on 4.12:
[root@pod2 /]# ip route
default via 10.244.0.3 dev eth0
10.96.0.0/16 via 10.244.0.1 dev eth0
10.244.0.0/24 dev eth0 proto kernel scope link src 10.244.0.5
10.244.0.0/16 via 10.244.0.1 dev eth0
^route pointing to .3

But the real DR IP is claimed as .4:
k8s.ovn.org/hybrid-overlay-distributed-router-gateway-ip: 10.244.0.4
.4 set in ARP flows:
cookie=0x0, duration=25.803s, table=0, n_packets=0, n_bytes=0, priority=100,arp,in_port=ext,arp_tpa=10.244.0.4,arp_op=1 actions=move:NXM_OF_ETH_SRC[]>NXM_OF_ETH_DST[],mod_dl_src:0a:58:0a:f4:00:03,load:0x2>NXM_OF_ARP_OP[],move:NXM_NX_ARP_SHA[]>NXM_NX_ARP_THA[],move:NXM_OF_ARP_SPA[]>NXM_OF_ARP_TPA[],load:0xa580af40003->NXM_NX_ARP_SHA[],load:0xaf40004->NXM_OF_ARP_SPA[],IN_PORT,resubmit(,1)