KVM: Do not migrate pending software interrupts.

INTn will be re-executed after migration. If we wanted to migrate
pending software interrupt we would need to migrate interrupt type
and instruction length too, but we do not have all required info on
SVM, so SVM->VMX migration would need to re-execute INTn anyway. To
make it simple never migrate pending soft interrupt.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>