Add LIST_FOREACH_SAFE, which is like LIST_FOREACH but allows you

to walk the list and remove the current item and destroy/free it.

Alexander Kabaev will likely do the equivalent for the other list
types, but I just happened to have this one sitting in a local
non-FreeBSD tree already.

sys/sys/queue.h

@@ -325,6 +325,13 @@ struct {								\
 	    (var);							\
 	    (var) = LIST_NEXT((var), field))
 
+#define LIST_FOREACH_SAFE(var, head, field, tvar)			\
+	for ((var) = LIST_FIRST((head)),				\
+	    (var) != NULL ? (tvar) = LIST_NEXT((var), field) : NULL;	\
+	    (var) != NULL;						\
+	    (var) = (tvar),						\
+	    (var) != NULL ? (tvar) = LIST_NEXT((var), field) : NULL)
+
 #define	LIST_INIT(head) do {						\
 	LIST_FIRST((head)) = NULL;					\
 } while (0)