Don't filter out TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (netty#9274)

Motivation:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 is supported since Java 8 (see https://docs.oracle.com/javase/8/docs/technotes/guides/security/SunProviders.html) and belongs to the recommended configurations in many references, eg SSLabs (https://github.com/ssllabs/research/wiki/SSL-and-TLS-Deployment-Best-Practices) or Google Cloud Platform Restricted Profile.

Modifications:

Add TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 to default ciphers list.

Result:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 is enabled by default.

handler/src/main/java/io/netty/handler/ssl/SslUtils.java

@@ -113,6 +113,7 @@ final class SslUtils {
         defaultCiphers.add("TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384");
         defaultCiphers.add("TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256");
         defaultCiphers.add("TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256");
+        defaultCiphers.add("TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384");
         defaultCiphers.add("TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA");
         // AES256 requires JCE unlimited strength jurisdiction policy files.
         defaultCiphers.add("TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA");