If rxthread is on, NAPI will call the kernel-thread context API (instead
of softirq context) API to transfer the packet to the stack.
Eventually, this part will be re-considered when multi-queue NAPI gets
in, which will eliminate the rx-thread.
Change-Id: Ib3d4d1450fb36f5c1e710802ceaab5d015e20c7d
CRs-Fixed: 957299