Samba: Creating share on a cifs mount fails

Initially reported at https://discuss.freedombox.org/t/how-to-share-an-existing-mount-point-with-samba-app/948

Trying to create an Open or Group share generated this error:
Error enabling share: (‘samba’, ‘’, ‘setfacl: /mnt/NAS/FreedomBox/shares/open_share: Operation not supported\nTraceback (most recent call last):\n File “/usr/share/plinth/actions/samba”, line 339, in \n main()\n File “/usr/share/plinth/actions/samba”, line 335, in main\n subcommand_method(arguments)\n File “/usr/share/plinth/actions/samba”, line 275, in subcommand_add_share\n arguments.windows_filesystem)\n File “/usr/share/plinth/actions/samba”, line 110, in _create_share\n _set_share_permissions(share_path)\n File “/usr/share/plinth/actions/samba”, line 265, in _set_share_permissions\n subprocess.check_call([‘setfacl’, ‘-Rdm’, ‘g::rwX’, directory])\n File “/usr/lib/python3.7/subprocess.py”, line 347, in check_call\n raise CalledProcessError(retcode, cmd)\nsubprocess.CalledProcessError: Command ‘[‘setfacl’, ‘-Rdm’, ‘g::rwX’, ‘/mnt/NAS/FreedomBox/shares/open_share’]’ returned non-zero exit status 1.\n’)