rmnet_data: Fix use-after-free in rmnet_vnd_create_dev

Currently it is possible for rmnet_vnd_create_dev to update features on
a free'd device in case of device registraton failure.

Fix this issue by updating features only on successful netdevice
registration.

Change-Id: Idbd50f91377206a73ef4105d35b2f5e8cc065a07
Signed-off-by: Ashwanth Goli <ashwanth@codeaurora.org>