Configuration of the posted interrupt descriptor is incorrect when devices
are hotplugged to the guest (and vcpus are halted).
See patch 4 for details.
---
v2: rather than using a potentially racy IPI (vs vcpu->cpu switches),
kick the vcpus when assigning a device and let the blocked per-CPU
list manipulation happen locally at ->pre_block and ->post_block
(Sean Christopherson).
