This commit fixes the following error with python3:

Traceback (most recent call last):
  File "_ctypes/callbacks.c", line 234, in 'calling callback function'
  File "/usr/lib/python3.6/site-packages/bcc/table.py", line 508, in raw_cb_
    callback(cpu, data, size)
  File "./opensnoop.py", line 169, in print_event
    if args.name and args.name not in event.comm:
TypeError: a bytes-like object is required, not 'str'
Signed-off-by: Gary Lin <glin@suse.com>