sched: always ask the scheduler to re-place the vcpu when the affinity changes

It's probably a good idea to re-evaluate placement whenever the
affinity changes.

This additionally has the benefit of removing scheduler-specific
exceptions introduced in git c/s e6a6fd63.

The conditionals surrounding vcpu_migrate() are left pending a re-work
of the logic to avoid the common case calling vcpu_migrate() twice (once
here, and once in context_saved().

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

xen/common/schedule.c

@@ -614,9 +614,10 @@ int vcpu_set_affinity(struct vcpu *v, const cpumask_t *affinity)
     vcpu_schedule_lock_irq(v);
 
     cpumask_copy(v->cpu_affinity, affinity);
-    if ( VCPU2OP(v)->sched_id == XEN_SCHEDULER_SEDF ||
-         !cpumask_test_cpu(v->processor, v->cpu_affinity) )
-        set_bit(_VPF_migrating, &v->pause_flags);
+
+    /* Always ask the scheduler to re-evaluate placement
+     * when changing the affinity */
+    set_bit(_VPF_migrating, &v->pause_flags);
 
     vcpu_schedule_unlock_irq(v);