net: rps: fix data stall after hotplug

When RPS is enabled, IPI is triggered to enqueue the backlog NAPI to
the poll list. If the CPU which was found to online in get_rps_cpus
is hotplugged after the NAPI_STATE_SCHED bit is set on
enqueue_to_backlog but before the IPI is delivered in
in net_rps_action_and_irq_enable, the poll list does not have the
backlog NAPI queued. As a consequence of this, dev_cpu_callback
does not clear the NAPI_STATE_SCHED bit on hotplug.

Since NAPI_STATE_SCHED is set even after the cpu comes back up,
packets get enqueued onto the input packet queue but are never
processed since the IPI will not be triggered.

This patch handles this race by unconditionally resetting the NAPI
state for the backlog NAPI on the offline CPU in dev_cpu_callback.

CRs-fixed: 817709
Change-Id: Ie73a21f4bb689948bfbbe1de10a1e9143e4424d2
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>