ref_count.h: In ref_count_obj_[inc dec], fix return value

Pointed-out-by: Sasha Kotchubievsky <sashakot@mellanox.com>

Signed-off-by: Hal Rosenstock <hal@mellanox.com>
ref_count.h: Add include of pthread.h

Pointed-out-by: Sasha Kotchubievsky <sashakot@mellanox.com>

Signed-off-by: Hal Rosenstock <hal@mellanox.com>