ax25: proc uid file misses header

This has been broken for a while. I happened to catch it testing because one
app "knew" that the top line of the calls data was the policy line and got
confused.

Put the header back.

Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>