netlink: make the scope string stable across libnl1-3

For globally scoped routes, libnl1 reports 'universe' and libnl3
reports 'global'. This patch makes sure that we only get 'global'.

Change-Id: I700ba3d0997a5c829c460753a300d4529aae2a61
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29598
Reviewed-by: Dan Kenigsberg <danken@redhat.com>