Update icmp6.h to current NetBSD.

This adds a few bits we need such as RFC 6106 support and the
definition of MLD_LISTENER_REDUCTION.

http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/netinet/icmp6.h?rev=1.47

Bug: 9469682
Change-Id: I97a4c2f0893012ce315334367c055097d0f8bb10
1 file changed