The shared counter template ib_counter_t uses the function
my_timer_cycles() as a source of pseudo-random numbers to pick a shard.
On some platforms, my_timer_cycles() could return the constant value 0.

get_rnd_value(): Remove.

my_pseudo_random(): Implement as an alias of my_timer_cycles() or
a wrapper for pthread_self().

Reviewed by: Vladislav Vaintroub