OSPF: Fix reconfiguration of vlinks

Fix crash during reconfiguration of OSPF config with vlinks. When vlink
is reconfigured, a generic iface-reconfiguration code is used, which in
one place supposes that it is running on a regular iface.

Thanks to Cybertinus for a bugreport.
32 jobs from int-new in 3 minutes and 23 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Image
passed #203461
dind allowed to fail
docker_centos-6-amd64

00:00:21

passed #203462
dind allowed to fail
docker_centos-7-amd64

00:00:21

passed #203451
dind allowed to fail
docker_debian-7-amd64

00:00:21

passed #203455
dind allowed to fail
docker_debian-7-i386

00:00:23

passed #203452
dind allowed to fail
docker_debian-8-amd64

00:00:21

passed #203456
dind allowed to fail
docker_debian-8-i386

00:00:21

passed #203453
dind allowed to fail
docker_debian-9-amd64

00:00:22

passed #203457
dind allowed to fail
docker_debian-9-i386

00:00:22

passed #203454
dind allowed to fail
docker_debian-testing-amd64

00:00:22

passed #203458
dind allowed to fail
docker_debian-testing-i386

00:00:21

passed #203459
dind allowed to fail
docker_fedora-25-amd64

00:00:22

passed #203460
dind allowed to fail
docker_fedora-26-amd64

00:00:23

passed #203463
dind allowed to fail
docker_opensuse-42_3-amd64

00:00:22

passed #203464
dind allowed to fail
docker_ubuntu-14_04-amd64

00:00:22

passed #203465
dind allowed to fail
docker_ubuntu-16_04-amd64

00:00:23

 
  Build
passed #203472
docker linux amd64
build-centos-6-amd64

00:01:03

passed #203473
docker linux amd64
build-centos-7-amd64

00:01:04

passed #203466
docker linux amd64
build-debian-7-amd64

00:01:05

passed #203477
docker linux amd64
build-debian-7-i386

00:00:48

passed #203467
docker linux amd64
build-debian-8-amd64

00:01:07

passed #203478
docker linux amd64
build-debian-8-i386

00:00:50

passed #203468
docker linux amd64
build-debian-9-amd64

00:01:07

passed #203479
docker linux amd64
build-debian-9-i386

00:00:53

passed #203469
docker linux amd64
build-debian-testing-amd64

00:01:08

passed #203480
docker linux amd64
build-debian-testing-i386

00:00:55

passed #203470
docker linux amd64
build-fedora-25-amd64

00:01:06

passed #203471
docker linux amd64
build-fedora-26-amd64

00:01:06

passed #203481
freebsd amd64
build-freebsd-11-amd64

00:01:57

passed #203482
freebsd i386
build-freebsd-11-i386

00:01:48

passed #203474
docker linux amd64
build-opensuse-42_3-amd64

00:01:04

passed #203475
docker linux amd64
build-ubuntu-14_04-amd64

00:01:06

passed #203476
docker linux amd64
build-ubuntu-16_04-amd64

00:00:45