include: Introduce typed params for virDomainSetIOThreadParams wrt pool size

include: Introduce typed params for virDomainSetIOThreadParams wrt pool size

Our public API offers virDomainSetIOThreadParams() function which
allows users to set various aspects of IOThreads. Introduce two
new typed parameters: VIR_DOMAIN_IOTHREAD_THREAD_POOL_MIN and
VIR_DOMAIN_IOTHREAD_THREAD_POOL_MAX which will allow users to
modify the thread-pool-min and thread-pool-max attributes of an
iothread.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>