Add netlink library as a dependency

To make dev target and to the release
Register for operstate changes in OS network ports

OF port has a flag `link_down` that indicates that a physical link is
not present in the port. We assume that the OF port is up (i.e. this flag
is not set) only if the operstate of the port is `up`.

More about the operstate can be found here:
https://www.kernel.org/doc/Documentation/networking/operstates.txt