bpf: Define sock security related BTF IDs under CONFIG_SECURITY_NETWORK

There are warnings reported from resolve_btfids when building vmlinux
with CONFIG_SECURITY_NETWORK disabled:

  WARN: resolve_btfids: unresolved symbol bpf_lsm_sk_free_security
  WARN: resolve_btfids: unresolved symbol bpf_lsm_sk_alloc_security

So only define BTF IDs for these LSM hooks when CONFIG_SECURITY_NETWORK
is enabled.

Fixes: c0c852dd ("bpf: Do not mark certain LSM hook arguments as trusted")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221217062144.2507222-1-houtao@huaweicloud.com

kernel/bpf/bpf_lsm.c

@@ -351,8 +351,10 @@ BTF_ID(func, bpf_lsm_bpf_prog_alloc_security)
 BTF_ID(func, bpf_lsm_bpf_prog_free_security)
 BTF_ID(func, bpf_lsm_file_alloc_security)
 BTF_ID(func, bpf_lsm_file_free_security)
+#ifdef CONFIG_SECURITY_NETWORK
 BTF_ID(func, bpf_lsm_sk_alloc_security)
 BTF_ID(func, bpf_lsm_sk_free_security)
+#endif /* CONFIG_SECURITY_NETWORK */
 BTF_ID(func, bpf_lsm_task_free)
 BTF_SET_END(untrusted_lsm_hooks)