perf script: Initialize callchain_param.record_mode

Milian Wolff reported non functional DWARF unwind under perf script. The
reason is that perf script does not properly configure
callchain_param.record_mode, which is needed by unwind code.

Stealing the code from report and leaving the place for more
initialization code in a hope we could merge it with
report__setup_sample_type one day.

Reported-by: Milian Wolff <mail@milianw.de>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Milian Wolff <milian.wolff@kdab.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20150813071724.GA21322@krava.brq.redhat.com


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