timer: fix reset return value

timer: fix reset return value

- API rte_timer_reset() should return -1 when the timer is in the
RUNNING or CONFIG state. Instead, it ignores the return value of
internal function __rte_timer_reset() and always returns 0.
We change rte_timer_reset() to return the value returned by
__rte_timer_reset().

- Enhance timer stress test 2 to report how many timer reset
collisions occur, i.e., how many times rte_timer_reset() fails
due to a timer being in the CONFIG state.

Signed-off-by: Robert Sanford <rsanford2@gmail.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>