KVM: nVMX: Fix conditions for NMI injection

The logic for checking if interrupts can be injected has to be applied
also on NMIs. The difference is that if NMI interception is on these
events are consumed and blocked by the VM exit.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>