proto: Connection side enum #5176

Job	Run time
test on netbsd	4m 52s
test on solaris	6h 0m 1s
audit	23s
lint	40s
msrv	1m 0s
test (ubuntu-latest, stable)	1m 37s
test-android (x86_64-linux-android, x86_64, 26)	2m 58s
test (ubuntu-latest, beta)	1m 12s
test-aws-lc-rs	1m 48s
test on freebsd	3m 59s
test-android (i686-linux-android, x86, 26)	2m 58s
test (macos-latest, stable)	1m 9s
test (windows-latest, stable)	5m 10s
test on illumos	6m 37s
test wasm32-unknown-unknown	53s
features (ubuntu-latest)	1h 26m 18s
features (macos-latest)	28m 56s
features (windows-latest)	51m 25s
	9h 21m 56s

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