cpus_allowed_policy fixups

- Make 'split' roundrobin the CPUs, if we have more threads
  than CPUs in the set.

- Properly use a CPU index, don't assume a sequential set of
  CPUs.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/os/os-freebsd.h b/os/os-freebsd.h
index 402792a..e35c835 100644
--- a/os/os-freebsd.h
+++ b/os/os-freebsd.h
@@ -32,6 +32,7 @@
 
 #define fio_cpu_clear(mask, cpu)        (void) CPU_CLR((cpu), (mask))
 #define fio_cpu_set(mask, cpu)          (void) CPU_SET((cpu), (mask))
+#define fio_cpu_isset(mask, cpu)	CPU_ISSET((cpu), (mask))
 #define fio_cpu_count(maks)		CPU_COUNT((mask))
 
 static inline int fio_cpuset_init(os_cpu_mask_t *mask)