apic_alloc_vector
u_int apic_alloc_vector(u_int apic_id, u_int irq);
new_vector = apic_alloc_vector(apic_id, intpin->io_irq);
vector = apic_alloc_vector(apic_id, msi->msi_irq);
vector = apic_alloc_vector(cpu, i);