tcp: Remove sk_protocol test for tcp_twsk_unique().

tcp: Remove sk_protocol test for tcp_twsk_unique().

Commit 383eed2de529 ("tcp: get rid of twsk_unique()") added
sk->sk_protocol test in  __inet_check_established() and
__inet6_check_established() to remove twsk_unique() and call
tcp_twsk_unique() directly.

DCCP has gone, and the condition is always true.

Let's remove the sk_protocol test.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250822190803.540788-2-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>