net: rps: fix cpu unplug

softnet_data.input_pkt_queue is protected by a spinlock that we must
hold when transferring packets from victim queue to an active one.
This is because other cpus could still be trying to enqueue packets
into victim queue.

A second problem is that when we transfert the NAPI poll_list from
victim to current cpu, we absolutely need to special case the percpu
backlog, because we do not want to add complex locking to protect
process_queue : Only owner cpu is allowed to manipulate it, unless
cpu is offline.

Based on initial patch from Prasad Sodagudi &
Subash Abhinov Kasiviswanathan.

This version is better because we do not slow down packet processing,
only make migration safer.

Change-Id: I6468cc74779b126ce0565f8bd6cc39514b14eb38
Reported-by: Prasad Sodagudi <psodagud@codeaurora.org>
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Git-commit: ac64da0b83d82abe62f78b3d0e21cca31aea24fa
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Trilok Soni <tsoni@codeaurora.org>