sys/netinet6/nd6.c: add ND6_IFF_ACCEPT_RTADV flag

[Jeffrey Hsu]

Hiroki Sato wrote:
Hi,

 Here is a patch to add the new flag ND6_IFF_ACCEPT_RTADV to
 implement a knob to contorol whether to accept RAs in per-interface
 basis (obtained from KAME via FreeBSD).


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Add a new flag "ND6_IFF_ACCEPT_RTADV" into nd_ifinfo to
control whether to accept RAs per-interface basis.
This flag is enabled by default.
Since the default behavior is the same, how useful is the
added functionality to optionally not accept RAs?  Also, is
there a corresponding change to ifconfig required?  Thanks.
						Jeffrey