Consistently use session_ctx for session caching.

The TLS 1.3 client logic used ctx instead. This is all moot as
SSL_set_SSL_CTX on a client really wouldn't work, but we should be
consistent. Unfortunately, this moves moving the pointer back to SSL
from SSL_CONFIG.

Change-Id: I45f8241e16f499ad416afd5eceb52dc82af9c4f4
Reviewed-on: https://boringssl-review.googlesource.com/27985
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/internal.h b/ssl/internal.h
index 2550aad..05a99b2 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -2649,10 +2649,6 @@
   size_t supported_group_list_len = 0;
   uint16_t *supported_group_list = nullptr;  // our list
 
-  // session_ctx is the |SSL_CTX| used for the session cache and related
-  // settings.
-  SSL_CTX *session_ctx = nullptr;
-
   // The client's Channel ID private key.
   EVP_PKEY *tlsext_channel_id_private = nullptr;
 
@@ -2755,6 +2751,10 @@
 
   SSL_CTX *ctx;
 
+  // session_ctx is the |SSL_CTX| used for the session cache and related
+  // settings.
+  SSL_CTX *session_ctx;
+
   // extra application data
   CRYPTO_EX_DATA ex_data;