'Parse the rssi info from the packet
:param self: An AccessPointFinder object
:param packet: A scapy.layers.RadioTap object
:type self: AccessPointFinder
:type packet: scapy.layers.RadioTap
:return: rssi
:rtype: int'

def _parse_rssi(self, packet):

    tmp = ord(packet.notdecoded[(-4):(-3)])
    tmp1 = ord(packet.notdecoded[(-2):(-1)])
    rssi = (- (256 - max(tmp, tmp1)))
    return rssi
