tcmsg: add hfsc support

With this patch, pyroute2 gets hfsc qdisc and class parsing, showing
things like the curve data the "stats app", etc. Example:

[{'attrs': [['TCA_KIND', 'hfsc'],
   ['TCA_OPTIONS', {}],
   ['TCA_STATS2',
    {'attrs': [['TCA_STATS_BASIC', {'bytes': 0, 'packets': 0}],
      ['TCA_STATS_QUEUE',
       {'backlog': 0, 'drops': 0, 'overlimits': 0, 'qlen': 0, 'requeues': 0}],
      ['TCA_STATS_APP', {'level': 1, 'period': 0, 'rtwork': 0, 'work': 0}]]}],
   ['TCA_STATS',
    {'backlog': 0,
     'bps': 0,
     'bytes': 0,
     'drop': 0,
     'overlimits': 0,
     'packets': 0,
     'pps': 0,
     'qlen': 0}],
   ['TCA_XSTATS',
    '00:30:26:05:00:88:ff:ff:a0:39:7d:99:00:88:ff:ff:8c:b9:33:81:ff:ff:ff:ff']],
  'event': 'RTM_NEWTCLASS',
  'family': 0,
  'handle': 2147680256,
  'index': 3,
  'info': 0,
  'pad1': 0,
  'pad2': 0,
  'parent': 4294967295},
 {'attrs': [['TCA_KIND', 'hfsc'],
   ['TCA_OPTIONS',
    {'attrs': [['TCA_HFSC_FSC', {'d': 0, 'm1': 0, 'm2': 10000000}],
      ['TCA_HFSC_USC', {'d': 0, 'm1': 0, 'm2': 50000000}]]}],
   ['TCA_STATS2',
    {'attrs': [['TCA_STATS_BASIC', {'bytes': 0, 'packets': 0}],
      ['TCA_STATS_QUEUE',
       {'backlog': 0, 'drops': 0, 'overlimits': 0, 'qlen': 0, 'requeues': 0}],
      ['TCA_STATS_APP', {'level': 0, 'period': 0, 'rtwork': 0, 'work': 0}]]}],
   ['TCA_STATS',
    {'backlog': 0,
     'bps': 0,
     'bytes': 0,
     'drop': 0,
     'overlimits': 0,
     'packets': 0,
     'pps': 0,
     'qlen': 0}],
   ['TCA_XSTATS',
    'c8:30:26:05:00:88:ff:ff:a0:39:7d:99:00:88:ff:ff:8c:b9:33:81:ff:ff:ff:ff']],
  'event': 'RTM_NEWTCLASS',
  'family': 0,
  'handle': 2147680257,
  'index': 3,
  'info': 0,
  'pad1': 0,
  'pad2': 0,
  'parent': 2147680256}]

Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>