[krbdev.mit.edu #2659] rpc code has no IPv6 support

[Greg Hudson via RT]

As of r24147, it is possible for callers to use libgssrpc with IPv6 
sockets provided that they:

  * Create and connect/bind their own sockets.
  * Only use TCP.
  * Do not query the addresses of client or server objects.

That's enough to get kadmin working, as noted in #6746.  There's no 
fundamental reason why UDP could not also be supported, but allowing the 
portmapper to be used might be difficult.

As I understand it, our libgssrpc is based on Sun's (now Oracle's) ONC 
RPC.  That API was updated to work with non-IPv4 transports and is now 
called TIRPC.  TIRPC has been incorporated into libc on the *BSD 
platforms and has also been ported to Linux (though not incorporated 
into glibc).

Our current understanding is that TIRPC code has been made available 
under two licenses: the SISSL and (via OpenSolaris) the CDDL.  Neither 
is believed to be GPL-compatible.  We are not aware of any 
implementations of TIRPC which are not derived from Sun/Oracle's code.  
We have made a request for the relevant parts of OpenSolaris to be 
relicensed under a BSD-like license so we might adapt it for the krb5 
tree.