OSPF: Fix wrong LSA collisions detection

In some circumstances (old LSA flushed but not acknowledged and not
removed) origination of a new LSA may wrongly triggers LSA collision
code. The patch fixes that.

Thanks to Asbjorn Mikkelsen for the bugreport and @mdelagueronniere
for the original patch.
32 jobs for <span class="ref-name">int-new</span> in 5 minutes and 47 seconds (queued for 1 minute and 27 seconds)
Status Job ID Name Coverage
  Image
passed #208808
dind allowed to fail
docker_centos-6-amd64

00:00:28

passed #208809
dind allowed to fail
docker_centos-7-amd64

00:00:25

passed #208798
dind allowed to fail
docker_debian-7-amd64

00:00:36

passed #208802
dind allowed to fail
docker_debian-7-i386

00:00:36

passed #208799
dind allowed to fail
docker_debian-8-amd64

00:00:36

passed #208803
dind allowed to fail
docker_debian-8-i386

00:00:36

passed #208800
dind allowed to fail
docker_debian-9-amd64

00:00:36

passed #208804
dind allowed to fail
docker_debian-9-i386

00:00:41

passed #208801
dind allowed to fail
docker_debian-testing-amd64

00:00:36

passed #208805
dind allowed to fail
docker_debian-testing-i386

00:00:40

passed #208806
dind allowed to fail
docker_fedora-25-amd64

00:00:40

passed #208807
dind allowed to fail
docker_fedora-26-amd64

00:00:37

passed #208810
dind allowed to fail
docker_opensuse-42_3-amd64

00:00:29

passed #208811
dind allowed to fail
docker_ubuntu-14_04-amd64

00:00:32

passed #208812
dind allowed to fail
docker_ubuntu-16_04-amd64

00:00:32

 
  Build
passed #208819
docker linux amd64
build-centos-6-amd64

00:00:42

passed #208820
docker linux amd64
build-centos-7-amd64

00:00:53

passed #208813
docker linux amd64
build-debian-7-amd64

00:00:49

passed #208824
docker linux amd64
build-debian-7-i386

00:00:55

passed #208814
docker linux amd64
build-debian-8-amd64

00:00:46

passed #208825
docker linux amd64
build-debian-8-i386

00:01:01

passed #208815
docker linux amd64
build-debian-9-amd64

00:01:27

passed #208826
docker linux amd64
build-debian-9-i386

00:00:53

passed #208816
docker linux amd64
build-debian-testing-amd64

00:01:35

passed #208827
docker linux amd64
build-debian-testing-i386

00:00:56

passed #208817
docker linux amd64
build-fedora-25-amd64

00:00:45

passed #208818
docker linux amd64
build-fedora-26-amd64

00:00:47

passed #208828
freebsd amd64
build-freebsd-11-amd64

00:01:54

passed #208829
freebsd i386
build-freebsd-11-i386

00:01:55

passed #208821
docker linux amd64
build-opensuse-42_3-amd64

00:00:54

passed #208822
docker linux amd64
build-ubuntu-14_04-amd64

00:00:55

passed #208823
docker linux amd64
build-ubuntu-16_04-amd64

00:00:46