The RPS code and "deferred skb free" both send IPI/ function call
to a remote CPU in which a softirq is raised. This leads to a warning on
PREEMPT_RT because raising softiqrs from function call led to undesired
behaviour in the past. I had duct tape in RT for the "deferred skb free"
and Wander Lairson Costa reported the RPS case.

Patch #1 creates per-CPU threads for the backlog NAPI. It follows the
	 threaded NAPI model and solves the issue and simplifies the
         code.
Patch #2 gets rid of the warning. Since the ksoftirqd changes the
         situtation isn't as bad as it was. Still, it would be better to
	 keep it in the context where it originated.

Sebastian