Suggest better defaults for `/etc/nftables.conf` #926

Job	Run time
build-test-binary	36s
test-on-docker (docker:24.0-dind, ubuntu-latest)	1m 25s
test-on-docker (docker:23.0-dind, ubuntu-latest)	1m 13s
test-on-docker (docker:20.10-dind, ubuntu-20.04)	1m 13s
test-on-docker (docker:19.03-dind, ubuntu-20.04)	59s
test-on-docker (docker:18.09-dind, ubuntu-20.04)	59s
test-on-docker (docker:18.06-dind, ubuntu-20.04)	1m 1s
	7m 26s

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