net: rmnet_data: Add support to configure custom device name

rmnet_data assigns device name by the order they are created.
This causes problems which multiple processes are trying to
create devices and leads to random device names.

Assign device name as specified by user.

CRs-Fixed: 2018785
Change-Id: Iab8e053c6ccacbeedaa7763e760d0c12e756b5d0
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>