selftests: drv-net: rss: validate min RSS table size

selftests: drv-net: rss: validate min RSS table size

Add a test which checks that the RSS table is at least 4x the max
queue count supported by the device. The original RSS spec from
Microsoft stated that the RSS indirection table should be 2 to 8
times the CPU count, presumably assuming queue per CPU. If the
CPU count is not a power of two, however, a power-of-2 table
2x larger than queue count results in a 33% traffic imbalance.
Validate that the indirection table is at least 4x the queue
count. This lowers the imbalance to 16% which empirically
appears to be more acceptable to memcache-like workloads.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260131225454.1225151-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>