rpc: simplify calling convention of virNetServerClientDispatchFunc
Currently virNetServerClientDispatchFunc implementations are only
responsible for free'ing the "msg" parameter upon success. Simplify the
calling convention by making it their unconditional responsibility to
free the "msg", and close the client if desired.
Reviewed-by: John Ferlan <jferlan@redhat.com> Reviewed-by: Jim Fehlig <jfehlig@suse.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>