XIA/United4ID: comply with Click XIA

Dan Barrett described the format of
the United4ID's XIDs as follows:

United4ID-4500000000010000fafa000000000000c0a81880

Byte  0: always 0x45
Byte  5: always 0x01
Byte  8: always 0xfa
Byte  9: always 0xfa
Bytes 16-19: IP address (192.168.24.128 in the above example)

All remaining bytes are always zero.