bpf: fix build without bpf_syscall

wrap bpf_stats_enabled sysctl with #ifdef
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 492ecee8 ("bpf: enable program stats")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/sysctl.c

@@ -224,9 +224,11 @@ static int proc_dostring_coredump(struct ctl_table *table, int write,
 #endif
 static int proc_dopipe_max_size(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp, loff_t *ppos);
+#ifdef CONFIG_BPF_SYSCALL
 static int proc_dointvec_minmax_bpf_stats(struct ctl_table *table, int write,
 					  void __user *buffer, size_t *lenp,
 					  loff_t *ppos);
+#endif
 
 #ifdef CONFIG_MAGIC_SYSRQ
 /* Note: sysrq code uses its own private copy */
@@ -1232,7 +1234,6 @@ static struct ctl_table kern_table[] = {
 		.extra1		= &one,
 		.extra2		= &one,
 	},
-#endif
 	{
 		.procname	= "bpf_stats_enabled",
 		.data		= &sysctl_bpf_stats_enabled,
@@ -1242,6 +1243,7 @@ static struct ctl_table kern_table[] = {
 		.extra1		= &zero,
 		.extra2		= &one,
 	},
+#endif
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
 	{
 		.procname	= "panic_on_rcu_stall",
@@ -3272,6 +3274,7 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
 
 #endif /* CONFIG_PROC_SYSCTL */
 
+#ifdef CONFIG_BPF_SYSCALL
 static int proc_dointvec_minmax_bpf_stats(struct ctl_table *table, int write,
 					  void __user *buffer, size_t *lenp,
 					  loff_t *ppos)
@@ -3293,7 +3296,7 @@ static int proc_dointvec_minmax_bpf_stats(struct ctl_table *table, int write,
 	}
 	return ret;
 }
-
+#endif
 /*
  * No sense putting this after each symbol definition, twice,
  * exception granted :-)