Possible bug with IPv6 ICMPv6 handling

[Doug Hardie]

I have found what to me seems like a bug with ICMPv6 handling in  
IPv6.  However, before submitting a PR I wanted to check to be sure  
that its not a misunderstanding on my part.

The network setup.  A host (A) connected to a router (B) connected to  
another host (C) on a separate network.  When all are up and running,  
A can ping6 to C and gets a response.  If you power off C and then do  
the ping again, tpcdump on A shows an ICMPv6 destination unreachable  
datagram received from B. However ping6 does not report that back to  
the user.  A ktrace of ping6 shows that it does not receive the ICMPv6  
response.  Its my understanding that it should and the ping6 code  
seems to imply that also. Is this a bug?