debug validation: introduce DEBUG_VALIDATE_BUG_ON

DEBUG_VALIDATE_BUG_ON(exp) will call BUG_ON(exp) if debug validation
is compiled in. Otherwise it's a no-op.

src/util-validate.h

@@ -96,11 +96,14 @@
     }                                               \
 } while(0)
 
+#define DEBUG_VALIDATE_BUG_ON(exp) BUG_ON((exp))
+
 #else /* DEBUG_VALIDATE */
 
 #define DEBUG_ASSERT_FLOW_LOCKED(f)
 #define DEBUG_VALIDATE_FLOW(f)
 #define DEBUG_VALIDATE_PACKET(p)
+#define DEBUG_VALIDATE_BUG_ON(exp)
 
 #endif /* DEBUG_VALIDATE */