Replace hash_current_message with get_current_message.

For TLS 1.3 draft 18, it will be useful to get at the full current
message and not just the body. Add a hook to expose it and replace
hash_current_message with a wrapper over it.

BUG=112

Change-Id: Ib9e00dd1b78e8b72e12409d85c80e96c5b411a8b
Reviewed-on: https://boringssl-review.googlesource.com/12238
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/dtls_method.c b/ssl/dtls_method.c
index 8026579..8e92cc9 100644
--- a/ssl/dtls_method.c
+++ b/ssl/dtls_method.c
@@ -132,7 +132,7 @@
     dtls1_new,
     dtls1_free,
     dtls1_get_message,
-    dtls1_hash_current_message,
+    dtls1_get_current_message,
     dtls1_release_current_message,
     dtls1_read_app_data,
     dtls1_read_change_cipher_spec,