SUNRPC: Eliminate PROC macro from rpcb_clnt

Clean up: Replace PROC macro with open coded C99 structure
initializers to improve readability.

The rpcbind v4 GETVERSADDR procedure is never sent by the current
implementation, so it is not copied to the new structures.

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