HEADS UP, minor change to IPv6 link local address setup

[gnn at freebsd.org]

Hi Folks,

I just committed to HEAD a minor change to our IPv6 support.  Unless a
user sets ipv6_enable to YES in rc.conf link local addresses will NOT
appear on any interface.  This seems to make some sense because you
shouldn't have them if you didn't ask for IPv6 to be enabled.  IPv6
remains in the kernel by default.

Please let me know if there are any issues with this change.  I did
test this but of course not as extensively as all of you can.

I intend to MFC this in 3 days if re@ is willing to let me.

Thanks,
George