Update: Finish adding functions to f_schedule.

Update: Finish adding functions to f_schedule.

This adds:
  - `f_schedule_affinity_get()`
  - `f_schedule_affinity_set()`
  - `f_schedule_attribute_get()`
  - `f_schedule_attribute_set()`
  - `f_schedule_policy_robin_interval_get()`
  - `f_schedule_priority_get_max()`
  - `f_schedule_priority_get_min()`
  - `f_schedule_yield()`

Note: the `f_schedule_attribute_get()` and `f_schedule_attribute_set()` have to use `syscall()` directly due to design problems with glibc.
The `struct sched_attr` is also an incomplete/broken type in glibc.
I have declared my own type based on the kernel structure.
It is unclear on how well this will work in practice.
I am also uncertain of the best way to mock a variadic function like `syscall()`.
The mocks for these are therefore incomplete.