New package: bwm-ng

Add new package: bwm-ng

Bandwidth Monitor NG is a small and console-based live network and
disk-io bandwidth monitor for Linux, BSD, Solaris, Mac OS X and others.

[Peter: move to net, fix Config.in line length, remove unused make var]
Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>