added if_log() and device_log()

[Adrian Chadd]

hi!

I just added if_log() and device_log(). They're log() variants of
if_printf() / device_printf() which will log to the kernel/syslog
buffer rather than do console output. That way syslog can decide
whether it needs to be printed or not.

I'm going to submit some patches soon to convert ath(4) and
net80211(4) to use if_log / device_log where appropriate so debugging
doesn't spam the console.

If you're writing device or interface logging/debugging and you want
to avoid the console, if_log() / device_log() is now your friend on
-HEAD.


-adrian