Merge branch 'fix-the-null-pointer-dereference-issue-in-bpf_lwt_xmit_push_encap'

Feng Yang says:

====================
Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap

Changes in v10:
- Patch simplification. Thanks, Martin KaFai Lau.
- Link to v9: https://lore.kernel.org/all/20260303074423.172680-1-yangfeng59949@163.com/
Changes in v9:
- Use dst_hold() and skb_dst_set().
  Skip !skb_dst check.
  Move all changes into the IS_ENABLED(CONFIG_IPV6).
  Use #if IS_ENABLED(CONFIG_IPV6); otherwise, a compilation error will occur when ipv6 is not enabled.
  Thanks, Martin KaFai Lau.
- Link to v8: https://lore.kernel.org/all/20260227082133.96951-1-yangfeng59949@163.com/
Changes in v8:
- set ret to an error code before goto out.
- Link to v7: https://lore.kernel.org/all/20260226095156.117996-1-yangfeng59949@163.com/
Changes in v7:
- Use ip6_null_entry to avoid. Thanks, Martin KaFai Lau.
Changes in v6:
- Modify the bpf_lwt_xmit_push_encap function and add selftests for it.
  Thanks, Martin KaFai Lau.
- Link to v5: https://lore.kernel.org/all/20260210090657.86977-1-yangfeng59949@163.com/
Changes in v5:
- Refer to the bpf_lwt_xmit_reroute function to configure the dst parameter.
- Link to v4: https://lore.kernel.org/all/20260209015111.28144-1-yangfeng59949@163.com/
Changes in v4:
- add rcu lock
- Link to v3: https://lore.kernel.org/all/20260206055113.63476-1-yangfeng59949@163.com/
Changes in v3:
- use dst_init
- Link to v2: https://lore.kernel.org/all/20260205092227.126665-1-yangfeng59949@163.com/
Changes in v2:
- Link to v1: https://lore.kernel.org/all/20260127084520.13890-1-luyun_611@163.com/
====================

Link: https://patch.msgid.link/20260304094429.168521-1-yangfeng59949@163.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>