On python3 map returns a generator instead of a list. This fixes the
following error:

Traceback (most recent call last):
  File "./ucalls", line 280, in <module>
    data = get_data()   # [(function, (num calls, latency in ns))]
  File "./ucalls", line 255, in get_data
    data.extend(syscalls)
AttributeError: 'map' object has no attribute 'extend'