Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.

Use sched_set_fifo() to request SCHED_FIFO and delegate
actual priority selection to userspace. Effectively no change in
behaviour.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>