SUNRPC: Use rpcbind version 2 GETPORT

Clean up: Change the version 2 procedure name to GETPORT.  It's the same
procedure number as GETADDR, but version 2 implementations usually refer
to it as GETPORT.

This also now matches the procedure name used in the version 2 procedure
entry in the rpcb_next_version[] array, making it slightly less confusing.

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