net: qualcomm: rmnet: Process packets over ethernet

Add support to send and receive packets over ethernet.
An example of usage is testing the data path on UML. This can be
achieved by setting up two UML instances in multicast mode and
associating rmnet over the UML ethernet device.

CRs-Fixed: 2156182
Change-Id: Ifad9cc8285e45067290b4dd9e05aa68628cfa65a
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>