Adding new package netdiscover an active/passive address reconnaissance ...

...tool, mainly developed for those wireless networks without dhcp server, when you are wardriving. It can be also used on hub/switched networks.
Can a test be added to do something more substantial than e.g. `--version` or `--help`? See `cmake.rb` for an example of an application formula with a good test and `tinyxml2.rb` for an example of a library formula with a good test. Thanks!