selftests: drv-net: fix linter warnings in pp_alloc_fail

selftests: drv-net: fix linter warnings in pp_alloc_fail

Fix linter warnings, it's a bit hard to check for new ones otherwise.

  W0311: Bad indentation. Found 16 spaces, expected 12 (bad-indentation)
  C0114: Missing module docstring (missing-module-docstring)
  W1514: Using open without explicitly specifying an encoding (unspecified-encoding)
  C0116: Missing function or method docstring (missing-function-docstring)

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20251007232653.2099376-8-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>