sunrpc: Turn list_for_each-s into the ..._entry-s

Saves some lines of code and some branticks when reading one.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>