Fix a typo in vm_domain_set(). When a domain crosses into the severe range,

we need to set the domain bit from the vm_severe_domains bitset (instead
of clearing it).

Reviewed by:	jeff, markj
Sponsored by:	Netflix, Inc.

sys/vm/vm_page.c

@@ -2845,7 +2845,7 @@ vm_domain_set(struct vm_domain *vmd)
 	}
 	if (!vmd->vmd_severeset && vm_paging_severe(vmd)) {
 		vmd->vmd_severeset = 1;
-		DOMAINSET_CLR(vmd->vmd_domain, &vm_severe_domains);
+		DOMAINSET_SET(vmd->vmd_domain, &vm_severe_domains);
 	}
 	mtx_unlock(&vm_domainset_lock);
 }