ieee802154: 6lowpan: ensure of sending 1280 packets
ieee802154: 6lowpan: ensure of sending 1280 packets

This patch changes the 1281 MTU to 1280. Others stack have only a 1280
byte array for uncompressed 6LoWPAN packets, this avoid that these
stacks have an overflow. Sending 1281 uncompressed 6LoWPAN packets isn't
also rfc complaint.

Signed-off-by: Alexander Aring <d03dbcdedb9639e397df9b8578e8fc8274f4e6c4@gmail.com>
Signed-off-by: Marcel Holtmann <44592b4eea36663c86b994bb0ea99d15309c1c7d@holtmann.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs