sdmsteppe: defconfig: Enable the l3mdev config

This change enable the kernel config to
allow route add support to local table from driver.
l3mdev feature allow driver to configure route using table
id.with this config driver is additing route to local table
for E2E data transfer.

Change-Id: Id696011f5b440a9d92e343b887b5beb879b52abb
Signed-off-by: Suraj Jaiswal <jsuraj@codeaurora.org>