SUNRPC: Move universal address definitions to global header

Universal addresses are defined in RFC 1833 and clarified in RFC 3530.  We
need to use them in several places in the NFS and RPC clients, so move the
relevant definition and block comment to an appropriate global include
file.

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