[lib] Fix timer precision.

[lib] Fix timer precision.

Whenever a thread adds an timer funcname_thread_add_timer_timeval() gets called
to add the timer. Before adding the timer a quagga_gettimeofday() call
is made to do some time house keeping. However quagga_gettimeofday() only
updates recent_time, not relative_time that is used to calculate
the alarm_time. Replace with quagga_get_relative (NULL)