Make python2.6-3.3 compatible and pep8 compliant.

Updated python code to be compatible with Python 2.6, 2.7 and 3.3
Done the same for the C code.

TODO: Move test_ethtool.py to python-nose (that has python2 and 3
support).

Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>