By this commit https://github.com/knative-sandbox/net-kourier/commit/ce84020add98cb9a051eee9df062d6711e1d64e7, Kourier controller determines where kourier-gateway is.
Our current operator deploys the Kourier in knative-serving-ingress or serverless-operator-ingress so we need to update the environmental variable.
This effects on serving v0.18+.