netlink: User libnl-3 when available

On new distibutions (Fedora, ubuntu, el7, etc) python-ethtool uses
libnl3 while vdsm was using libnl1. The problem was that libnl1
and libnl3 use the same algorithm for allocating netlink ports and
collided. This patch fixes it by using libnl3 if ethtool uses it.

Change-Id: I45f043a8416e57d5fb550e2e817e6df38cd793b1
Bug-Url: https://bugzilla.redhat.com/1078312
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26514
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>