swrap: Allow to pass 8 fds

Python 3.14 is sending 8 file descriptors around for concurrent code.

SWRAP_ERROR[python3 (54391)] - swrap_sendmsg_unix_scm_rights: cmsg->cmsg_len=48,size_fds_in=32 => num_fds_in=8 > SWRAP_MAX_PASSED_FDS(6)

REASON: Exception: Exception: Traceback (most recent call last):
  File "/builddir/build/BUILD/samba-4.23.0-build/samba-4.23.0rc3/bin/python/samba/tests/docs.py", line 266, in test_default_s3
    self._test_default(['bin/testparm'])
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/samba-4.23.0-build/samba-4.23.0rc3/bin/python/samba/tests/docs.py", line 323, in _test_default
    future = executor.submit(check_or_set_smbconf_default, cmdline, self.topdir, param, default)
  File "/usr/lib64/python3.14/concurrent/futures/process.py", line 816, in submit
    self._adjust_process_count()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/usr/lib64/python3.14/concurrent/futures/process.py", line 775, in _adjust_process_count
    self._spawn_process()
    ~~~~~~~~~~~~~~~~~~~^^
  File "/usr/lib64/python3.14/concurrent/futures/process.py", line 793, in _spawn_process
    p.start()
    ~~~~~~~^^
  File "/usr/lib64/python3.14/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)
                  ~~~~~~~~~~~^^^^^^
  File "/usr/lib64/python3.14/multiprocessing/context.py", line 300, in _Popen
    return Popen(process_obj)
  File "/usr/lib64/python3.14/multiprocessing/popen_forkserver.py", line 35, in __init__
    super().__init__(process_obj)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/usr/lib64/python3.14/multiprocessing/popen_fork.py", line 20, in __init__
    self._launch(process_obj)
    ~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/usr/lib64/python3.14/multiprocessing/popen_forkserver.py", line 51, in _launch
    self.sentinel, w = forkserver.connect_to_new_process(self._fds)
                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/usr/lib64/python3.14/multiprocessing/forkserver.py", line 113, in connect_to_new_process
    reduction.sendfds(client, allfds)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.14/multiprocessing/reduction.py", line 146, in sendfds
    sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, fds)])
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 22] Invalid argument