modprobe: prefix libkmod messages to stderr with modprobe:

modprobe: prefix libkmod messages to stderr with modprobe:

When we are logging to stderr we are previously relying on libkmod
sending it to the default location in case we are not asked to log to
syslog. The problem is that modprobe may be used in scripts that don't
want to log to syslog (since they are not daemons, like scripts to
generate initrd) and then it's difficult to know where the message comes
from.

This patch treats only the messages coming from libkmod.