kernel/bpf/syscall: fix warning defined but not used

There will be a build warning -Wunused-function if CONFIG_CGROUP_BPF
isn't defined, since the only user is inside #ifdef CONFIG_CGROUP_BPF:
kernel/bpf/syscall.c:1229:12: warning: ‘bpf_prog_attach_check_attach_type’
    defined but not used [-Wunused-function]
 static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Current code moves function bpf_prog_attach_check_attach_type inside
ifdef CONFIG_CGROUP_BPF.

Fixes: 5e43f899b03a ("bpf: Check attach type at prog load time")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/syscall.c

@@ -1226,18 +1226,6 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
 	}
 }
 
-static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
-					     enum bpf_attach_type attach_type)
-{
-	switch (prog->type) {
-	case BPF_PROG_TYPE_CGROUP_SOCK:
-	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
-		return attach_type == prog->expected_attach_type ? 0 : -EINVAL;
-	default:
-		return 0;
-	}
-}
-
 /* last field in 'union bpf_attr' used by this command */
 #define	BPF_PROG_LOAD_LAST_FIELD expected_attach_type
 
@@ -1465,6 +1453,18 @@ out_free_tp:
 
 #ifdef CONFIG_CGROUP_BPF
 
+static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
+					     enum bpf_attach_type attach_type)
+{
+	switch (prog->type) {
+	case BPF_PROG_TYPE_CGROUP_SOCK:
+	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
+		return attach_type == prog->expected_attach_type ? 0 : -EINVAL;
+	default:
+		return 0;
+	}
+}
+
 #define BPF_PROG_ATTACH_LAST_FIELD attach_flags
 
 static int sockmap_get_from_fd(const union bpf_attr *attr,