Merge branch 'xfrm: interface: Add unstable helpers for XFRM metadata'

Eyal Birger says:

====================

This patch series adds xfrm metadata helpers using the unstable kfunc
call interface for the TC-BPF hooks.

This allows steering traffic towards different IPsec connections based
on logic implemented in bpf programs.

The helpers are integrated into the xfrm_interface module. For this
purpose the main functionality of this module is moved to
xfrm_interface_core.c.
---

changes in v6: fix sparse warning in patch 2
changes in v5:
  - avoid cleanup of percpu dsts as detailed in patch 2
changes in v3:
  - tag bpf-next tree instead of ipsec-next
  - add IFLA_XFRM_COLLECT_METADATA sync patch
====================

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