fpga: rfnoc: Regenerate noc_shells

Original-commit: 6ff8bd326b0da4d2f9e044a3df3e19b807459d25

lib/rfnoc/blocks/rfnoc_block_null_src_sink/noc_shell_null_src_sink.v

@@ -1,5 +1,5 @@
 //
-// Copyright 2021 Ettus Research, a National Instruments Brand
+// Copyright 2022 Ettus Research, a National Instruments Brand
 //
 // SPDX-License-Identifier: LGPL-3.0-or-later
 //
@@ -15,6 +15,7 @@
 //   THIS_PORTID : Control crossbar port to which this block is connected
 //   CHDR_W      : AXIS-CHDR data bus width
 //   MTU         : Maximum transmission unit (i.e., maximum packet size in
+//                 CHDR words is 2**MTU).
 //
 
 `default_nettype none