This patch avoids setting an irq while loading the state of the ISA bridge.
Because the i8259 has not been deserialized yet, raising an interrupt
could bring the system out-of-sync with the migration source.  For example,
the migration source could have masked the interrupt in the i8259. On the
destination, the i8259 device model would not know that yet and would
trigger an interrupt in the CPU.

This patch eliminates setting the irq and just restores the calculated
state fields in post_load function.  Interrupt state will be deserialized
separately through the IRR field of the i8259.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>