Split ssl_read_bytes hook into app_data and close_notify hooks.

This still needs significant work, especially the close_notify half, but
clarify the interface and get *_read_bytes out of SSL_PROTOCOL_METHOD.
read_bytes is an implementation detail of those two and get_message
rather than both an implementation detail of get_message for handshake
and a (wholly inappropriate) exposed interface for the other two.

BUG=468889

Change-Id: I7dd23869e0b7c3532ceb2e9dd31ca25ea31128e7
Reviewed-on: https://boringssl-review.googlesource.com/4956
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index d898cf2..4a9ae83 100644
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -671,6 +671,14 @@
   return 1;
 }
 
+int ssl3_read_app_data(SSL *ssl, uint8_t *buf, int len, int peek) {
+  return ssl3_read_bytes(ssl, SSL3_RT_APPLICATION_DATA, buf, len, peek);
+}
+
+void ssl3_read_close_notify(SSL *ssl) {
+  ssl3_read_bytes(ssl, 0, NULL, 0, 0);
+}
+
 /* Return up to 'len' payload bytes received in 'type' records.
  * 'type' is one of the following:
  *