So that it's done when the vcpu_id has been set. For the BSP the
vcpu_id is set at SUB_INTR, while for the APs it's done in
init_secondary_tail that's called at SUB_SMP order FIRST.
Reported and tested by: cperciva
Approved by: re (gjb)
Sponsored by: Citrix Systems R&D
Differential revision: https://reviews.freebsd.org/D17013
fae9a0cb9b