net: qualcomm: rmnet: Move rmnet_mode to rmnet_port

Mode information on the real device makes it easier to route packets
to rmnet device or bridged device based on the configuration.

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>