what do jails map 127.0.0.1 to?

I am finally back to looking at an old PR#205193.

The problem is that the nfsuserd daemon expects upcalls from the kernel
that are from localhost (127.0.0.1) and when jails are running on the system,
127.0.0.1 is mapped to some other IP#. (I think it might be the address of the
first net interface on the machine, but I'm not sure?)

Is there a way that nfsuserd.c can find out what this IP# is?
(I have a patch that converts nfsuserd.c to using an AF_LOCAL socket, but that
 breaks for some setups. I think it was when the directory the socket was being
 created in is NFSv4 mounted, but I can't remember exactly how it fails.)

Thanks for any help with this, rick