bpf: tcp: Fix type confusion in sol_tcp_sockopt().

bpf: tcp: Fix type confusion in sol_tcp_sockopt().

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

  socket(AF_INET, SOCK_RAW, IPPROTO_TCP)

Let's use sk_is_tcp().

Note that initially sol_tcp_sockopt() checked sk->sk_prot->setsockopt.

Fixes: 2ab42c7b871f ("bpf: Check the protocol of a sock to agree the calls to bpf_setsockopt().")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20260504210610.180150-7-kuniyu@google.com