Docs: FIB iteration macros

 * Basic FIB operations are performed by functions defined by this module,

 * enumerating of FIB contents is accomplished by using the FIB_WALK() macro

 * or FIB_ITERATE_START() if you want to do it asynchronously.

 *

 * For simple iteration just place the body of the loop between FIB_WALK() and

 * FIB_WALK_END(). You can't modify the FIB during the iteration (you can modify

 * data in the node, but not add or remove nodes).

 *

 * If you need more freedom, you can use the FIB_ITERATE_*() group of macros.

 * First, you initialize an iterator with FIB_ITERATE_INIT(). Then you can put

 * the loop body in between FIB_ITERATE_START() and FIB_ITERATE_END(). In

 * addition, the iteration can be suspended by calling FIB_ITERATE_PUT().

 * This'll link the iterator inside the FIB. While suspended, you may modify the

 * FIB, exit the current function, etc. To resume the iteration, enter the loop

 * again. You can use FIB_ITERATE_UNLINK() to unlink the iterator (while

 * iteration is suspended) in cases like premature end of FIB iteration.

 *

 * Note that the iterator must not be destroyed when the iteration is suspended,

 * the FIB would then contain a pointer to invalid memory. Therefore, after each

 * FIB_ITERATE_INIT() or FIB_ITERATE_PUT() there must be either

 * FIB_ITERATE_START() or FIB_ITERATE_UNLINK() before the iterator is destroyed.

 */

#undef LOCAL_DEBUG