6lowpan: fix process_data return values

As process_data now returns just error codes fix up the calls to this
function to only drop the skb if an error code is returned.

Signed-off-by: Martin Townsend <mtownsend1973@gmail.com>
Acked-by: Alexander Aring <alex.aring@gmail.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

diff --cc net/bluetooth/6lowpan.c
Simple merge

diff --cc net/ieee802154/6lowpan_rtnl.c
Simple merge