Prepare for adding IPv6 support to the RPC client by adding IPv6
capabilities to rpcbind.  Note that this is support on the query side
only; registering IPv6 addresses with the local portmapper will come
later.

Note we have to take care not to fall back to using version 2 of the
rpcbind protocol if we're dealing with IPv6 address.  Version 2 doesn't
support IPv6 at all.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: Aurelien Charbon <aurelien.charbon@ext.bull.net>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>