examples/ubuntu: add netlink network provider

This report the network state using netlink kernel interface thru
libnl-3.0 and allow us to remove the dependencies on network manager
command line tools.

Bug: 24466635
Change-Id: Icebc38a68522ad24a6f7cdad6e22cf39ce098ffa
Reviewed-on: https://weave-review.googlesource.com/1246
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
Reviewed-by: Alex Vakulenko <avakulenko@google.com>