perf evsel: Set attr.task bit for a tracking event

perf evsel: Set attr.task bit for a tracking event

The perf_event_attr.task bit is to track task (fork and exit) events but
it missed to be set by perf_evsel__config().  While it was not a problem
in practice since setting other bits (comm/mmap) ended up being in same
result, it'd be good to set it explicitly anyway.

The attr->task is to track task related events (fork/exit) only but
other meta events like comm and mmap[2] also needs the task events.  So
setting attr->comm and/or attr->mmap causes the kernel emits the task
events anyway.  So the attr->task is only meaningful when other bits are
off but I'd like to set it for completeness.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1422518843-25818-6-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>