net: rmnet_data: Support for NETLINK getters

Added support for RMNET_NETLINK_GET_LOGICAL_EP_CONFIG
and RMNET_NETLINK_GET_NETWORK_DEVICE_ASSOCIATED in the
rmnet_data configuration module.

CRs-fixed: 599231
Change-Id: Ib5eeb4a37f80a4df19cb3c1ef02ec477f5445740
Acked-by: David Arinzon <darinzon@qti.qualcomm.com>
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>