net: rmnet_data: Add NAPI context for rmnet_data devices

This is needed so that we can pass the virtual netdevice NAPI struct
to napi_gro_receive rather than relying on the current CPU NAPI
context which can cause issues due to CPU hotplug.

Change-Id: I41977c3a3a51212aa2fe092427b0ca924045b477
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>