io_uring/zcrx: selftests: switch to using defer() for cleanup

Switch to using defer() for putting the NIC back to the original state
prior to running the selftest.

Signed-off-by: David Wei <dw@davidwei.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250425022049.3474590-2-dw@davidwei.uk


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