Merge branch 'fix-ntuple-rules-targeting-default-rss'

Gal Pressman says:

====================
Fix ntuple rules targeting default RSS

This series addresses a regression in ethtool flow steering where rules
targeting the default RSS context (context 0) were incorrectly rejected.

The default RSS context always exists but is not stored in the rss_ctx
xarray like additional contexts. The current validation logic was
checking for the existence of context 0 in this array, causing valid
flow steering rules to be rejected.

This prevented configurations such as:
- High priority rules directing specific traffic to the default context
- Low priority catch-all rules directing remaining traffic to additional
  contexts

Patch 1 fixes the validation logic to skip the existence check for
context 0.

Patch 2 adds a selftest that verifies this behavior.

v3: https://lore.kernel.org/20250609120250.1630125-1-gal@nvidia.com
v2: https://lore.kernel.org/20250225071348.509432-1-gal@nvidia.com
====================

Link: https://patch.msgid.link/20250612071958.1696361-1-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>