USN-4467-3: QEMU regression

USN-4467-1 fixed vulnerabilities in QEMU. The fix for CVE-2020-13754 introduced a regression in certain environments. This update fixes the problem. We apologize for the inconvenience. Original advisory details: Ren Ding, Hanqing Zhao, Alexander Bulekov, and Anatoly Trosinenko discovered that the QEMU incorrectly handled certain msi-x mmio operations. An attacker inside a guest could possibly use this issue to cause QEMU to crash, resulting in a denial of service. (CVE-2020-13754)