selftests: rss_drv: Add RSS indirection table resize tests

Add resize tests to rss_drv.py. Devices without dynamic table sizing
are skipped via _require_dynamic_indir_size().

resize_periodic: set a periodic 4-entry table, shrink channels to
fold, grow back to unfold. Check the exact pattern is preserved. Has
main and non-default context variants.

resize_below_user_size_reject: send a periodic table with user_size
between the big and small device table sizes. Verify that shrinking
below user_size is rejected even though the table is periodic. Has
main and non-default context variants.

resize_nonperiodic_reject: set a non-periodic table (equal N), verify
that channel reduction is rejected.

resize_nonperiodic_no_corruption: verify a failed resize leaves both
the indirection table contents and the channel count unchanged.

Signed-off-by: Björn Töpel <bjorn@kernel.org>
Link: https://patch.msgid.link/20260320085826.1957255-5-bjorn@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>