credit: generalize __vcpu_has_soft_affinity()

As pointed out in the discussion of the patch at
http://lists.xenproject.org/archives/html/xen-devel/2015-02/msg03256.html
generalizing the conditions here means code elsewhere doesn't need to
take into consideration internals of how load balancing in the credit
scheduler works.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Use VCPU2ONLINE(vc) (or really an open coded variant thereof)
    instead of cpu_online_map (suggested by Dario).

--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -292,11 +292,10 @@ __runq_remove(struct csched_vcpu *svc)
 static inline int __vcpu_has_soft_affinity(const struct vcpu *vc,
                                            const cpumask_t *mask)
 {
-    if ( cpumask_full(vc->cpu_soft_affinity)
-         || !cpumask_intersects(vc->cpu_soft_affinity, mask) )
-        return 0;
-
-    return 1;
+    return !cpumask_subset(cpupool_online_cpumask(vc->domain->cpupool),
+                           vc->cpu_soft_affinity) &&
+           !cpumask_subset(vc->cpu_soft_affinity, vc->cpu_hard_affinity) &&
+           cpumask_intersects(vc->cpu_soft_affinity, mask);
 }
 
 /*