[AX25]: Kill user triggable printks.

sfuzz can easily trigger any of those.

move the printk message to the corresponding comment: makes the
intention of the code clear and easy to pick up on an scheduled
removal.  as bonus simplify the braces placement.

Signed-off-by: maximilian attems <max@stro.at>
Signed-off-by: David S. Miller <davem@davemloft.net>