bpf: Emit struct bpf_tcp_sock type in vmlinux BTF

In one of our internal testing, we found a case where
  - uapi struct bpf_tcp_sock is in vmlinux.h where vmlinux.h is not
    generated from the testing kernel
  - struct bpf_tcp_sock is not in vmlinux BTF

The above combination caused bpf load failure as the following
memory access
  struct bpf_tcp_sock *tcp_sock = ...;
  ... tcp_sock->snd_cwnd ...
needs CORE relocation but the relocation cannot be resolved since
the kernel BTF does not have corresponding type.

Similar to other previous cases (nf_conn___init, tcp6_sock, mctcp_sock, etc.),
add the type to vmlinux BTF with BTF_EMIT_TYPE macro.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230502180543.1832140-1-yhs@fb.com

net/core/filter.c

@@ -6916,6 +6916,8 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 					FIELD));			\
 	} while (0)
 
+	BTF_TYPE_EMIT(struct bpf_tcp_sock);
+
 	switch (si->off) {
 	case offsetof(struct bpf_tcp_sock, rtt_min):
 		BUILD_BUG_ON(sizeof_field(struct tcp_sock, rtt_min) !=