selftests: drv-net: iou-zcrx: allocate hugepages for large chunks test

selftests: drv-net: iou-zcrx: allocate hugepages for large chunks test

The large chunks test needs 2MB hugepages for its mmap allocation,
but the test system may not have any pre-allocated. Ensure at least
64 hugepages are available before running the test, and restore the
original value on cleanup.

While at it strip the stdout, it has a trailing new line.

Before: ok 5 iou-zcrx.test_zcrx_large_chunks # SKIP Can't allocate huge pages
Link: https://patch.msgid.link/20260227171305.2848240-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>