1. There is a regression issue in the ARP code. The incomplete
ARP entry was timing out too quickly (1 second timeout), as
such, a new entry is created each time arpresolve() is called.
Therefore the maximum attempts made is always 1. Consequently
the error code returned to the application is always 0.
2. Set the expiration of each incomplete entry to a 20-second
lifetime.
3. Return "incomplete" entries to the application.
Reviewed by: kmacy
MFC after: 3 days