5704 libzfs can only handle 255 filedescriptors

*** 522,526 ****
--- 522,531 ----
      'zvol_misc_004_pos', 'zvol_misc_005_neg', 'zvol_misc_006_pos']
  
  [/opt/zfs-tests/tests/functional/zvol/zvol_swap]
  tests = ['zvol_swap_001_pos', 'zvol_swap_002_pos', 'zvol_swap_003_pos',
      'zvol_swap_004_pos', 'zvol_swap_005_pos', 'zvol_swap_006_pos']
+ 
+ [/opt/zfs-tests/tests/functional/libzfs]
+ tests = ['many_fds']
+ pre =
+ post =