perf trace beauty: Alias 'umount' to 'umount2'

Before:

  # perf trace -e *mount* umount /dev/mapper/fedora-home /s
    11.576 ( 0.004 ms) umount/3138 umount2(arg0: 94501956754656, arg1: 0, arg2: 1, arg3: 140051050083104, arg4: 4, arg5: 94501956755136) = -1 EINVAL Invalid argument
  #

After:

  # perf trace -e *mount* umount /s
     0.000 ( 9.241 ms): umount/5251 umount2(name: 0x55f74a986480) = 0

Signed-off-by: Benjamin Peterson <benjamin@python.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180828035344.31500-1-benjamin@python.org


[ split from a larger patch ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>