net: qualcomm: rmnet: Allow to configure flags for new devices

Add an option to configure the rmnet aggregation and command features
on device creation. This is achieved by using the vlan flags option.

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