netlink: move netlink into a lib vdsm subpackage

netlink.py was increasingly getting new netlink entities making the
module difficult to follow. This patch splits each entity on a
separate module of a netlink package so that each new module is
easy to reason about.

Change-Id: I9b393588ccb3ac0c4529446c285570f49cdb1e28
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27472
Reviewed-by: Dan Kenigsberg <danken@redhat.com>