selftests: drv-net: test RSS header field configuration

Test reading RXFH fields over IOCTL and netlink.

  # ./tools/testing/selftests/drivers/net/hw/rss_api.py
  TAP version 13
  1..3
  ok 1 rss_api.test_rxfh_indir_ntf
  ok 2 rss_api.test_rxfh_indir_ctx_ntf
  ok 3 rss_api.test_rxfh_fields
  # Totals: pass:3 fail:0 xfail:0 xpass:0 skip:0 error:0

Link: https://patch.msgid.link/20250708220640.2738464-6-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>