Create bytes from properties

def to_bytes(self):
        '''
        Create bytes from properties
        '''
        # Verify that the properties make sense
        self.sanitize()

        # Write the next header type
        bitstream = BitStream('uint:8=%d' % self.next_header)

        # Add the reserved bits
        bitstream += BitStream(8)

        # Add the fragment offset
        bitstream += BitStream('uint:13=%d' % self.fragment_offset)

        # Add the reserved bits
        bitstream += BitStream(2)

        # Add the flags
        bitstream += BitStream('bool=%d' % self.more_fragments)

        # Add the identification
        bitstream += BitStream('uint:32=%d' % self.identification)

        return bitstream.bytes + bytes(self.payload)