criu_opts contains rpc options and notify callback,
so we can keep all options in just one structure.
This will allow us to easily extend libcriu functionality
and yet keep all options in one place.

We're also not hiding rpc opts structure anymore, so
it is pretty clear where power-user should put his own
CriuOpts instance if he would like to do that.
Signed-off-by: Ruslan Kuprieiev <rkuprieiev@cloudlinux.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>