net: msm_rmnet: Add an extended ioctl definition to pass xlat device info

Add an ioctl for passing rmnet_data device name to the physical device
driver for xlat capable calls. This information is used by the driver
to optimize traffic on the rmnet_data device.

CRs-Fixed: 762178
Change-Id: Ib19730d239882f0900ca2dbd91e5252fefd63053
Acked-by: Sudharsan Coimbatore Premkumar <supremku@qti.qualcomm.com>
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>