Comment 1 for bug 1844652

Steps to exercise this codepath:

PRJ=$(openstack project show demo -f value -c id)
openstack router create --project $PRJ router2 >/dev/null
RTR=$(openstack router show router2 -f value -c id)

# this external network may already exist..
openstack network create public --external --default --provider-network-type flat --provider-physical-network public >/dev/null 2>&1 || true
EXT_NET_ID=$(openstack network show public -f value -c id)

openstack network create --external --provider-network-type geneve public2 >/dev/null 2>&1
EXT_NET_ID2=$(openstack network show public2 -f value -c id)
openstack subnet create --ip-version 4 --network $EXT_NET_ID2 --subnet-range 192.168.111.0/24 --no-dhcp public2-subnet1 >/dev/null

openstack router set --external-gateway $EXT_NET_ID $RTR
openstack router show $RTR | grep -i external

openstack router set --external-gateway $EXT_NET_ID2 $RTR
openstack router show $RTR | grep -i external

openstack router unset --external-gateway $RTR
openstack router show $RTR | grep -i external