perf evsel: Inform how to make a sysctl setting permanent

perf evsel: Inform how to make a sysctl setting permanent

When a tool can't open counters due to the kernel.perf_event_paranoit
sysctl setting, we inform how to tweak it to allow the operation to
succeed, in addition to that, suggest setting /etc/sysctl.conf to
make the setting permanent.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-4gwe99k4a6p12d4u8bbyttj2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>