tools: add IFLA_XFRM_COLLECT_METADATA to uapi/linux/if_link.h

Needed for XFRM metadata tests.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Link: https://lore.kernel.org/r/20221203084659.1837829-4-eyal.birger@gmail.com


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>