Continue UDP/UDPv6 synchronization project:
Continue UDP/UDPv6 synchronization project:

- Fix copyrights, comments in UDPv6.
- Remove macro defines for in6pcb and udp6stat.
- Consistently refer to inpcbs as 'inp' and not also 'in6p'.

Reviewed by:	gnn, jinmei, bz
Approved by:	re (bmah)

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