Several changes to the timeout API, simplifying the code and allowing
more simplification later.

 * TO_ANN_INTERVAL renamed to TO_ANN_SEND (as opposed to TO_ANN_RECEIPT)

 * TO_SYNC renamed to TO_SYNC_SEND for symmetry with above

 * added timeout_init() to take not of the waiting values

 * timeout_set now receives only the index, not the value (see above)

 * __timeout_set added for those that want a specific value

 * timeout_rand is gone, as timeout_set knows which to randomize

 * all users fixed
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>