io_uring/zcrx: selftests: fix setting ntuple rule into rss

Fix ethtool syntax for setting ntuple rule into rss. It should be
`context' instead of `action'.

Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://patch.msgid.link/20250503043007.857215-1-dw@davidwei.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>