selftests: drv-net: iou-zcrx: wait for memory cleanup of probe run

selftests: drv-net: iou-zcrx: wait for memory cleanup of probe run

The large chunks test does a probe run of iou-zcrx before it runs the
actual test. After the probe run finishes, the context will still exist
until the deferred io_uring teardown. When running iou-zcrx the second
time, io_uring_register_ifq() can return -EEXIST due to the existence of
the old context.

The fix is simple: wait for the context teardown using the new
mp_clear_wait() utility before running the second instance of iou-zcrx.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Link: https://patch.msgid.link/20260305080446.897628-2-dtatulea@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>