Merge branch 'bpf-tcp-fix-type-confusion-in-bpf-helper-functions'

Kuniyuki Iwashima says:

====================
bpf: tcp: Fix type confusion in bpf helper functions.

bpf_tcp_sock() only check if sk->sk_protocol is IPPROTO_TCP,
but RAW socket can bypass it:

  socket(AF_INET, SOCK_RAW, IPPROTO_TCP)

The same issues exist in other bpf functions:

  * bpf_mptcp_sock_from_subflow()
  * bpf_skc_to_tcp_sock()
  * bpf_skc_to_tcp6_sock()
  * sol_tcp_sockopt()

Patch 1 fixes bpf_tcp_sock() and Patch 2 adds a test for it.
Patch 3 ~ 6 fix the rest of the functions above.

Changes:
  v2:
    * Inverse if (err) to if (!err) in the selftest
    * Add patch 3 ~ 6

  v1: https://lore.kernel.org/bpf/20260430184405.1227386-1-kuniyu@google.com/
      https://lore.kernel.org/mptcp/20260430-mptcp-bpf-mptcp-sock-type-v1-1-d2ed5cda7da9@kernel.org/
====================

Link: https://patch.msgid.link/20260504210610.180150-1-kuniyu@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>