codegen: Fix enums.h generation with python3

Trying to generate enums.h with python3 results in
Traceback (most recent call last):
  File "./spice_codegen.py", line 217, in <module>
    write_enums(writer, options.generate_dissector)
  File "./spice_codegen.py", line 99, in write_enums
    write_channel_enums(writer, c, False, False)
  File "./spice_codegen.py", line 17, in write_channel_enums
    if len(messages) == 0:
TypeError: object of type 'filter' has no len()

filter() returns an enumerator object in python3 while it used to return
a list in python2. Using list(filter()) instead fixes that error.
I've checked that the generated enums.h is identical with python2 and
python3.

0 files changed, 0 insertions, 0 deletions