Add a new battery meter for the *BSD.
Support DragonFly BSD 3.4 in netmeter.

DragonFly 3.4 gathers per-cpu network statistics.
Use correct sized integer for sysctl return value.
Remove unused variable.
Use snprintf() instead of std::ostringstream when updating speed in loadmeter.
Make loadmeter autoscaling predictable.

Previously, loadmeter total was adjusted to current load or five times that, which made it to drift. This patch always adjust the total to powers-of-two.