Use 32-bit values, not 16, for IP ID values.

IP ID fields are overloaded to include the flow label of IPv6 packets.
In particular, abstract_ip_hdr is no longer limited to 16 bits.
Use 32-bit IP IDs in idle scan code.

Part of Mathias Morbitzer's patch from
http://seclists.org/nmap-dev/2013/q3/135.
IPv6 idle scan patch by Mathias Morbitzer.

http://seclists.org/nmap-dev/2013/q3/549
Kill Id change.
Add list of IPv6 fragment sequence generation algorithms.

http://seclists.org/nmap-dev/2013/q3/369
CHANGELOG for IPv6 idle scan.