Restore rate limiting of connections opening #3992

Job	Run time
check-features	3m 12s
cargo-deny (bans licenses sources)	27s
cargo-spellcheck	22s
check-no-std	1m 33s
check-rustdoc-links	48s
clippy	38s
fmt	34s
fuzzing-binaries-compile	8m 34s
test-32bits	6m 5s
test-64bits	12m 8s
wasm-node-check	2m 2s
wasm-node-versions-match	30s
all-ci	1s
	36m 54s

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