selftests: drv-net: rss_ctx: add tests for RSS configuration and contexts

Add tests focusing on indirection table configuration and
creating extra RSS contexts in drivers which support it.

  $ export NETIF=eth0 REMOTE_...
  $ ./drivers/net/hw/rss_ctx.py
  KTAP version 1
  1..8
  ok 1 rss_ctx.test_rss_key_indir
  ok 2 rss_ctx.test_rss_context
  ok 3 rss_ctx.test_rss_context4
  # Increasing queue count 44 -> 66
  # Failed to create context 32, trying to test what we got
  ok 4 rss_ctx.test_rss_context32 # SKIP Tested only 31 contexts, wanted 32
  ok 5 rss_ctx.test_rss_context_overlap
  ok 6 rss_ctx.test_rss_context_overlap2
  # .. sprays traffic like a headless chicken ..
  not ok 7 rss_ctx.test_rss_context_out_of_order
  ok 8 rss_ctx.test_rss_context4_create_with_cfg
  # Totals: pass:6 fail:1 xfail:0 xpass:0 skip:1 error:0

Note that rss_ctx.test_rss_context_out_of_order fails with the device
I tested with, but it seems to be a device / driver bug.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240626012456.2326192-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>