perf trace: Sort syscalls stats by msecs in --summary

perf trace: Sort syscalls stats by msecs in --summary

  # trace -a -s sleep 1
  <SNIP>
   Xorg (1965), 788 events, 19.0%, 0.000 msec

     syscall            calls    total       min       avg       max      stddev
                                 (msec)    (msec)    (msec)    (msec)        (%)
     --------------- -------- --------- --------- --------- ---------     ------
     select                89   731.038     0.000     8.214   175.218     36.71%
     ioctl                 22     0.661     0.010     0.030     0.072     10.43%
     writev                42     0.253     0.002     0.006     0.011      5.94%
     recvmsg               60     0.185     0.001     0.003     0.009      5.90%
     setitimer             60     0.127     0.001     0.002     0.006      6.14%
     read                  52     0.102     0.001     0.002     0.005      8.55%
     rt_sigprocmask        45     0.092     0.001     0.002     0.023     23.65%
     poll                  12     0.021     0.001     0.002     0.003      7.21%
     epoll_wait            12     0.019     0.001     0.002     0.002      2.71%

   firefox (10871), 1080 events, 26.1%, 0.000 msec

     syscall            calls    total       min       avg       max      stddev
                                 (msec)    (msec)    (msec)    (msec)        (%)
     --------------- -------- --------- --------- --------- ---------     ------
     poll                 240   979.562     0.000     4.082    17.132     11.33%
     recvmsg              240     0.532     0.001     0.002     0.007      3.69%
     read                  60     0.303     0.003     0.005     0.029      8.50%

Suggested-by: Milian Wolff <milian.wolff@kdab.com>
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-52kdkuyxihq0kvc0n2aalhay@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>