Extract message-consuming code-path to separate function

The first part of the function ssl_read_record_layer() was
to mark the previous message as consumed. This commit moves
the corresponding code-path to a separate static function
ssl_consume_current_message().
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index b8f2715..23a5bdd 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4283,6 +4283,9 @@
  * RFC 6347 4.1.2.7) and continue reading until a valid record is found.
  *
  */
+
+/* Helper functions for mbedtls_ssl_read_record(). */
+static int ssl_consume_current_message( mbedtls_ssl_context *ssl );
 static int ssl_read_record_layer( mbedtls_ssl_context *ssl );
 
 int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
@@ -4334,13 +4337,9 @@
     return( 0 );
 }
 
-static int ssl_read_record_layer( mbedtls_ssl_context *ssl )
+static int ssl_consume_current_message( mbedtls_ssl_context *ssl )
 {
-    int ret;
-
     /*
-     * Step A
-     *
      * Consume last content-layer message and potentially
      * update in_msglen which keeps track of the contents'
      * consumption state.
@@ -4422,6 +4421,25 @@
         ssl->in_msglen = 0;
     }
 
+    return( 0 );
+}
+
+static int ssl_read_record_layer( mbedtls_ssl_context *ssl )
+{
+    int ret;
+
+    /*
+     * Step A
+     *
+     * Consume last content-layer message and potentially
+     * update in_msglen which keeps track of the contents'
+     * consumption state.
+     */
+
+    ret = ssl_consume_current_message( ssl );
+    if( ret != 0 )
+        return( ret );
+
     /*
      * Step B
      *