DS-Lite support for EIM, EIF, AP-P, and hairpinning

DS-Lite now supports:

• EIM (Endpoint Independent Mapping) -- EIM ensures that the source address and port are always mapped to the same address and port, irrespective of destination IP address and port.
• EIF (Endpoint Independent Filtering) -- EIF enables incoming traffic if at least one outgoing packet was sent and mapping has not timed out.
• AP-P (Address Pooling Paired ) -- AP-P guarantees that an IP address is always mapped to the same IP address irrespective of port numbers
• Hairpinning -- Packets exiting one softwire can go back on another softwire after twice NAT processing. This is usually the case when one host behind the softwire initiator (B4) tries to communicate with a host behind another B4.