EXP: ARP APN discovery avoid broadcast originator IP addresses

[nadicek]

Originator IP address in ARP request is generated in +1 manner from the APN IP address (we got this from DNS), this can result in generating a broadcast address which is not correct.

• Avoid broadcast address by trying +1/-1 while the generated address is not a broadcast address
• Save the generated originator address into APN object
• source: iPerf_magic.py