#289 Legacy-Possible failed ARP updates if PEP Pub IF bound to multiple addresses

[John A. Sullivan III]

It is possible to generate random ARP update failures if a PEP has the same Public Interface bound to more than one network because SubRangeOptions::dynamicARPChanges() only matches the network on the interface in order to find the subnet mask to use for the address binding. If multiple networks are bound to the same interface with different subnet masks, it could use the wrong mask.