proto: Connection side enum #5200

Job	Run time
test on illumos	6m 47s
test on netbsd	4m 55s
audit	22s
features (ubuntu-latest)	1h 16m 53s
lint	1m 8s
features (macos-latest)	23m 35s
msrv	1m 1s
features (windows-latest)	51m 1s
test (ubuntu-latest, stable)	1m 29s
test (ubuntu-latest, beta)	1m 14s
test-android (x86_64-linux-android, x86_64, 26)	2m 46s
test-aws-lc-rs	1m 42s
test (macos-latest, stable)	1m 11s
test on freebsd	4m 14s
test (windows-latest, stable)	4m 21s
test-android (i686-linux-android, x86, 26)	2m 44s
test on solaris	11m 29s
test wasm32-unknown-unknown	59s
	3h 17m 51s

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