vkernel - Fix lockup with [v]kernel due to missing ipiq signal

vkernel - Fix lockup with [v]kernel due to missing ipiq signal

* If the target ipiq has nothing but passively queued entries the target
  cpu will normally just process the ipi's on the next clock interrupt.

  However, if the originating cpu is forced to live-loop waiting for the
  target to the drain the target may not be aware that it needs to drain
  ASAP.

* The fix is for the originating cpu to ensure that an ipi interrupt is
  sent to the target cpu before live looping.

* This appears to primarily effect vkernels.

Reported-by: ftigeot, tuxillo