perf inject: Set branch stack feature flag when synthesizing branch stacks

The branch stack feature flag is set by 'perf record' when recording
data that contains branch stacks.  Consequently, when 'perf inject'
synthesizes branch stacks, the feature flag should be set also.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1443186956-18718-13-git-send-email-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>