KVM: nVMX: Fix posted intr delivery when vcpu is in guest mode

The PI vector for L0 and L1 must be different. If dest vcpu0
is in guest mode while vcpu1 is delivering a non-nested PI to
vcpu0, there wont't be any vmexit so that the non-nested interrupt
will be delayed.

Signed-off-by: Wincy Van <fanwenyi0529@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>