Add pr_fmt macro to spell out the source of messages in prefix.
Before this patch:
packet size is too long (1543 > 1518)
With this patch:
af_packet: packet size is too long (1543 > 1518)
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>