Merge branch 'fix-unique-field-logic-in-btf'

Kumar Kartikeya Dwivedi says:

====================
Fix unique field logic in BTF

Fix constraint of certain fields that have to be unique when nested
structs are present, BPF_REFCOUNT which should be marked as unique.
See commit logs for details. While at it, fix improper offset check.

Changelog:
----------
v1 -> v2
v1: https://lore.kernel.org/bpf/20260719142401.2420111-1-memxor@gmail.com

 * Add fix for BPF_REFCOUNT not being unique. (Sashiko)
 * Roll improper offset warning check into series. (Sashiko)
====================

Link: https://patch.msgid.link/20260719153634.2908692-1-memxor@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>