[vioserial] Update MSI interrupt limit

[kostyanf14]

Resolves: https://issues.redhat.com/browse/RHEL-21792

[YanVugenfirer]

Just to add some comment - maybe if CI is still not running, even in the commit message: up until now when several ports were used only one MSI interrupt would be used.

[vrozenfe]

IMHO the driver will not get any benefits from this patch due to the way how the DPC routine is implemented for this driver.
Originally it was designed to work with IRQL interrupt and DPC just goes through the list of the active posts and polls in and out queues. If I'm not mistaken, when the MSI support was added the developer who did it decided to keep the same way of working for the new MSI interrupts mechanism. So it doesn't matter how many MSI the driver claims, it will only increase the potential number or resources that the driver needs, but not improve the way how ISR-DPC chain implemented in this driver.

In any case this patch seems to be absolutely harmless and if you want to merged it then it's fine with me.

Vadim.