selftests: drv-net: rss_ctx: Add test for ntuple rules targeting default RSS context

selftests: drv-net: rss_ctx: Add test for ntuple rules targeting default RSS context

Add test_rss_default_context_rule() to verify that ntuple rules can
correctly direct traffic to the default RSS context (context 0).

The test creates two ntuple rules with explicit location priorities:
- A high-priority rule (loc 0) directing specific port traffic to
  context 0.
- A low-priority rule (loc 1) directing all other TCP traffic to context
  1.

This validates that:
1. Rules targeting the default context function properly.
2. Traffic steering works as expected when mixing default and
   additional RSS contexts.

The test was written by AI, and reviewed by humans.

Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20250612071958.1696361-3-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>