core: Rmnet initial commit

Inital commit of rmnet_core net device driver in dlkm form
in datarmnet. This requires rmnet to be disabled in the
kernel and for it to be loaded before dependent modules.

CRs-Fixed: 2558810
Change-Id: I742e85033fa0999bf9069d43ce73ab9a622a8388
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>