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: c0c852dd1876 ("bpf: Do not mark certain LSM hook arguments as trusted")
Signed-off-by: Hou Tao <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

kernel/bpf/bpf_lsm.c

···
 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)