code: def extract_protocol(self):
          
          if self.present.mcs:
              return '.11n'
  
          if self.present.vht:
              return '.11ac'
  
          if self.present.channel and hasattr(self, 'chan'):
              if self.chan.five_g:
                  if self.chan.ofdm:
                      return '.11a'
              elif self.chan.two_g:
                  if self.chan.cck:
                      return '.11b'
                  elif self.chan.ofdm or self.chan.dynamic:
                      return '.11g'
          return 'None'
docs: extract 802.11 protocol from radiotap.channel.flags
          :return: str
              protocol name
              one of below in success
              [.11a, .11b, .11g, .11n, .11ac]
              None in fail