Add NETLINK support to probe for interfaces/addresses on Linux

[troglobit]

The current 10 sec probe mechanism can be optimized by adding netlink monitor support for detecting interfaces and addresses being added to and removed from the system.

Note: patches that add dependency on an external library will not be accepted. Instead, see https://github.com/troglobit/finit/blob/master/plugins/netlink.c which I recommend adapting.