Merge branch 'support-skf_net_off-and-skf_ll_off-on-skb-frags'

Willem de Bruijn says:

====================
support SKF_NET_OFF and SKF_LL_OFF on skb frags

From: Willem de Bruijn <willemb@google.com>

Address a longstanding issue that may lead to missed packets
depending on system configuration.

Ensure that reading from packet contents works regardless of skb
geometry, also when using the special SKF_.. negative offsets to
offset from L2 or L3 header.

Patch 2 is the selftest for the fix.

v2->v3
  - do not remove bpf_internal_load_pointer_neg_helper, because it
    is still used in the sparc32 JIT

v1->v2
  - introduce bfp_skb_load_helper_convert_offset to avoid open
    coding
  - selftest: add comment why early demux must be disabled

v2: https://lore.kernel.org/netdev/20250404142633.1955847-1-willemdebruijn.kernel@gmail.com/
v1: https://lore.kernel.org/netdev/20250403140846.1268564-1-willemdebruijn.kernel@gmail.com/
====================

Link: https://patch.msgid.link/20250408132833.195491-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>