MFC:

• Disabled responding to NI queries from a global address by default as specified in RFC4620. A new flag for icmp6_nodeinfo was added to enable the feature.
• Also cleaned up the code so that the semantics of the icmp6_nodeinfo flags is clearer (i.e., defined specific macro names instead of using hard-coded values).

Approved by: gnn (mentor)

src/sys/netinet/icmp6.h: 1.21
src/sys/netinet6/icmp6.c: 1.76
src/sys/netinet6/in6_proto.c: 1.43