Rename Channel ID's EncryptedExtensions to just ChannelID in C.

To match the Go side. That message will never be used for anything else,
so there's not much need to give it such a long name.

Change-Id: I3396c9d513d02d873e59cd8e81ee64005c5c706c
Reviewed-on: https://boringssl-review.googlesource.com/8620
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

include/openssl/ssl3.h

@@ -404,7 +404,7 @@ OPENSSL_COMPILE_ASSERT(
 #define SSL3_MT_CERTIFICATE_STATUS 22
 #define SSL3_MT_SUPPLEMENTAL_DATA 23
 #define SSL3_MT_NEXT_PROTO 67
-#define SSL3_MT_CHANNEL_ID_ENCRYPTED_EXTENSIONS 203
+#define SSL3_MT_CHANNEL_ID 203
 #define DTLS1_MT_HELLO_VERIFY_REQUEST 3
 
 /* The following are legacy aliases for consumers which use

ssl/handshake_client.c

@@ -1987,8 +1987,7 @@ static int ssl3_send_channel_id(SSL *ssl) {
   }
 
   CBB cbb, body, child;
-  if (!ssl->method->init_message(ssl, &cbb, &body,
-                                 SSL3_MT_CHANNEL_ID_ENCRYPTED_EXTENSIONS) ||
+  if (!ssl->method->init_message(ssl, &cbb, &body, SSL3_MT_CHANNEL_ID) ||
       !CBB_add_u16(&body, TLSEXT_TYPE_channel_id) ||
       !CBB_add_u16_length_prefixed(&body, &child) ||
       !BN_bn2cbb_padded(&child, 32, x) || !BN_bn2cbb_padded(&child, 32, y) ||

ssl/handshake_server.c

@@ -2029,7 +2029,7 @@ static int ssl3_get_channel_id(SSL *ssl) {
   BIGNUM x, y;
   CBS encrypted_extensions, extension;
 
-  n = ssl->method->ssl_get_message(ssl, SSL3_MT_CHANNEL_ID_ENCRYPTED_EXTENSIONS,
+  n = ssl->method->ssl_get_message(ssl, SSL3_MT_CHANNEL_ID,
                                    ssl_dont_hash_message, &ok);
 
   if (!ok) {