We use evsel->sample_size to detect underflows in
perf_evsel__parse_sample, but we were failing to update it after
perf_evsel__init(), i.e. when we decide, after creating an evsel, that
we want some extra field bit set.

Fix it by introducing methods to set a bit that will take care of
correctly adjusting evsel->sample_size.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-2ny5pzsing0dcth7hws48x9c@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>