code: def strip_seq_cntrl(self, idx):
          
          seq_cntrl = struct.unpack('H', self._packet[idx:idx + 2])[0]
          seq_num = seq_cntrl >> 4
          frag_num = seq_cntrl & 0x000f
          return seq_num, frag_num
docs: strip(2 byte) wlan.seq(12 bit) and wlan.fram(4 bit)
          number information.
          :seq_cntrl: ctypes.Structure
          :return: int
              sequence number
          :return: int
              fragment number