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: 2ab42c7 ("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

Author: q2ven

net/core/filter.c

@@ -5481,7 +5481,7 @@ static int sol_tcp_sockopt(struct sock *sk, int optname,
 			   char *optval, int *optlen,
 			   bool getopt)
 {
-	if (sk->sk_protocol != IPPROTO_TCP)
+	if (!sk_is_tcp(sk))
 		return -EINVAL;
 
 	switch (optname) {