6149 use NULL capable segop as a shorthand for no-capabilities

@@ -1996,10 +1996,13 @@
 }
 
 int
 segop_capable(struct seg *seg, segcapability_t cap)
 {
+        if (seg->s_ops->capable == NULL)
+                return (0);
+
         return (seg->s_ops->capable(seg, cap));
 }
 
 int
 segop_inherit(struct seg *seg, caddr_t addr, size_t len, uint_t op)