Move peer_supported_group_list to SSL_HANDSHAKE.

Now not only the pointers but also the list itself is released after the
handshake completes.

Change-Id: I8b568147d2d4949b3b0efe58a93905f77a5a4481
Reviewed-on: https://boringssl-review.googlesource.com/11528
Reviewed-by: Adam Langley <agl@google.com>

ssl/internal.h

diff --git a/ssl/internal.h b/ssl/internal.h
index 1efc486..591e6ab 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -943,6 +943,12 @@
   /* num_peer_sigalgs is the number of entries in |peer_sigalgs|. */
   size_t num_peer_sigalgs;
 
+  /* peer_supported_group_list contains the supported group IDs advertised by
+   * the peer. This is only set on the server's end. The server does not
+   * advertise this extension to the client. */
+  uint16_t *peer_supported_group_list;
+  size_t peer_supported_group_list_len;
+
   /* session_tickets_sent, in TLS 1.3, is the number of tickets the server has
    * sent. */
   uint8_t session_tickets_sent;