perf_counter: Rename perf_counter_limit sysctl

Rename perf_counter_limit to perf_counter_max_sample_rate and
prohibit creation of counters with a known higher sample
frequency.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 386be91..95c797c 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -650,7 +650,7 @@
 
 extern int sysctl_perf_counter_paranoid;
 extern int sysctl_perf_counter_mlock;
-extern int sysctl_perf_counter_limit;
+extern int sysctl_perf_counter_sample_rate;
 
 extern void perf_counter_init(void);