[3.5] Fix panic in etcd validate secure endpoints

[fuweid]

Backport: #13824
Closes: #13810

NOTE: There are too many commits in the original pull request. I can't just use cherry-pick -xs to carry it.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[ahrtr]

Should this PR be backported to 3.4? Could you double check?

Please also add a changelog item, thx

[fuweid]

Should this PR be backported to 3.4? Could you double check?

etcd/pkg/transport/transport.go

Line 34 in 3253d5c

Dial: (&net.Dialer{

3.4 uses Dail so it won't panic.
And I use the same test in release-3.4 and it passes. I think we don't need to backport for 3.4.

➜  transport git:(release-3.4) ✗ git show | head -n 1
commit 420669a504281517c3de9d5ab234f62714984b24
➜  transport git:(release-3.4) ✗ go test -v -run=TestValidateSecureEndpoints -count=1 ./
=== RUN   TestValidateSecureEndpoints
{"level":"info","msg":"created cert file","path":"/tmp/etcd-test-tls-3358351632/cert.pem"}
{"level":"info","msg":"created key file","path":"/tmp/etcd-test-tls-3358351632/key.pem"}
=== RUN   TestValidateSecureEndpoints/invalidEndPoints
=== RUN   TestValidateSecureEndpoints/insecureEndpoints
=== RUN   TestValidateSecureEndpoints/secureEndPoints
=== RUN   TestValidateSecureEndpoints/mixEndPoints
--- PASS: TestValidateSecureEndpoints (0.01s)
    --- PASS: TestValidateSecureEndpoints/invalidEndPoints (0.00s)
    --- PASS: TestValidateSecureEndpoints/insecureEndpoints (0.00s)
    --- PASS: TestValidateSecureEndpoints/secureEndPoints (0.00s)
    --- PASS: TestValidateSecureEndpoints/mixEndPoints (0.00s)
PASS
ok      go.etcd.io/etcd/pkg/transport   0.014s
➜  transport git:(release-3.4) ✗

Please also add a changelog item, thx

Sure. Please check this #16566

[ahrtr]

thx

[jmhbnz]

LGTM Thanks @fuweid