commit d0c22119 upstream.

The mesh forwarding path was not checking that data
frames were protected when running an encrypted network;
add the necessary check.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>