Description of problem:
When gnutls receives multiple (e.g. 32) KeyUpdate messages on a connection, it closes the connection

Version-Release number of selected component (if applicable):
gnutls-3.6.5-2.el8.x86_64

How reproducible:
always

Steps to Reproduce:
1. run test-tls13-keyupdate.py from tlsfuzzer
2.
3.

Actual results:
multiple KeyUpdate messages ...
Error encountered while processing node <tlsfuzzer.messages.KeyUpdateGenerator object at 0x7f7534ebc828> (child: <tlsfuzzer.messages.KeyUpdateGenerator object at 0x7f7534ebc860>) with last message being: <tlslite.messages.KeyUpdate object at 0x7f753299f518>
Error while processing
Traceback (most recent call last):
  File "/root/tlsfuzzer/tlsfuzzer/runner.py", line 234, in run
    self.state.msg_sock.sendMessageBlocking(msg)
  File "/root/tlsfuzzer/tlslite/messagesocket.py", line 186, in sendMessageBlocking
    for _ in self.sendMessage(msg):
  File "/root/tlsfuzzer/tlslite/messagesocket.py", line 181, in sendMessage
    for res in self.flush():
  File "/root/tlsfuzzer/tlslite/messagesocket.py", line 121, in flush
    for res in self.sendRecord(msg):
  File "/root/tlsfuzzer/tlslite/recordlayer.py", line 630, in sendRecord
    for result in self._recordSocket.send(encryptedMessage, padding):
  File "/root/tlsfuzzer/tlslite/recordlayer.py", line 103, in send
    for result in self._sockSendAll(data):
  File "/root/tlsfuzzer/tlslite/recordlayer.py", line 69, in _sockSendAll
    bytesSent = self.sock.send(data)
  File "/root/tlsfuzzer/tlslite/bufferedsocket.py", line 34, in send
    return self.socket.send(data)
BrokenPipeError: [Errno 32] Broken pipe

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "scripts/test-tls13-keyupdate.py", line 575, in main
    runner.run()
  File "/root/tlsfuzzer/tlsfuzzer/runner.py", line 248, in run
    raise AssertionError("Unexpected closure from peer")
AssertionError: Unexpected closure from peer


Expected results:
OK

Additional info: