This is intended to be used by devices and network devices
to log things to the kernel syslog rather than hand-rolling
log() stuff (like what happens in other places in net/if.c)
or being very spammy with device_printf()/printf() (like, well,
a lot of things.)

I've used this in my local tree to convert net80211 and ath_hal
logging over to log at INFO/DEBUG where appropriate and it
works quite well. On devices with serial consoles (ie, all the
weird things I use in my wifi test bed here) writing debug
information to the serial console causes quite bad behaviour.