netconsole: Convert to pr_<level>

Use a more current logging style.

Convert printks to pr_<level>.

Consolidate multiple printks into a single printk to avoid
any possible dmesg interleaving.  Add a default "event" msg
in case the listed types are ever expanded.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>