SUNRPC: Remove duplicate universal address generation

RPC universal address generation is currently done in several places:
rpcb_clnt.c, nfs4proc.c xprtsock.c, and xprtrdma.c.  Remove the
redundant cases that convert a socket address to a universal
address.  The nfs4proc.c case takes a pre-formatted presentation
address string, not a socket address, so we'll leave that one.

Because the new uaddr constructor uses the recently introduced
rpc_ntop(), it now supports proper "::" shorthanding for IPv6
addresses.  This allows the kernel to register properly formed
universal addresses with the local rpcbind service, in _all_ cases.

The kernel can now also send properly formed universal addresses in
RPCB_GETADDR requests, and support link-local properly when
encoding and decoding IPv6 addresses.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>