BGP: Cleanup channels when going down

When going up, uncleaned old channel state may trigger unexpected
conditions crashing bird.
32 jobs for master in 3 minutes and 47 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Image
passed #225283
dind allowed to fail
docker_centos-6-amd64

00:00:26

passed #225284
dind allowed to fail
docker_centos-7-amd64

00:00:28

passed #225273
dind allowed to fail
docker_debian-7-amd64

00:00:30

passed #225277
dind allowed to fail
docker_debian-7-i386

00:00:32

passed #225274
dind allowed to fail
docker_debian-8-amd64

00:00:30

passed #225278
dind allowed to fail
docker_debian-8-i386

00:00:30

passed #225275
dind allowed to fail
docker_debian-9-amd64

00:00:30

passed #225279
dind allowed to fail
docker_debian-9-i386

00:00:30

passed #225276
dind allowed to fail
docker_debian-testing-amd64

00:00:32

passed #225280
dind allowed to fail
docker_debian-testing-i386

00:00:30

passed #225281
dind allowed to fail
docker_fedora-25-amd64

00:00:31

passed #225282
dind allowed to fail
docker_fedora-26-amd64

00:00:32

passed #225285
dind allowed to fail
docker_opensuse-42_3-amd64

00:00:27

passed #225286
dind allowed to fail
docker_ubuntu-14_04-amd64

00:00:29

passed #225287
dind allowed to fail
docker_ubuntu-16_04-amd64

00:00:30

 
  Build
passed #225294
docker linux amd64
build-centos-6-amd64

00:00:59

passed #225295
docker linux amd64
build-centos-7-amd64

00:01:00

passed #225288
docker linux amd64
build-debian-7-amd64

00:01:20

passed #225299
docker linux amd64
build-debian-7-i386

00:01:06

passed #225289
docker linux amd64
build-debian-8-amd64

00:01:23

passed #225300
docker linux amd64
build-debian-8-i386

00:00:52

passed #225290
docker linux amd64
build-debian-9-amd64

00:01:07

passed #225301
docker linux amd64
build-debian-9-i386

00:00:51

passed #225291
docker linux amd64
build-debian-testing-amd64

00:01:07

passed #225302
docker linux amd64
build-debian-testing-i386

00:00:54

passed #225292
docker linux amd64
build-fedora-25-amd64

00:01:00

passed #225293
docker linux amd64
build-fedora-26-amd64

00:01:03

passed #225303
freebsd amd64
build-freebsd-11-amd64

00:02:01

passed #225304
freebsd i386
build-freebsd-11-i386

00:01:48

passed #225296
docker linux amd64
build-opensuse-42_3-amd64

00:01:03

passed #225297
docker linux amd64
build-ubuntu-14_04-amd64

00:01:04

passed #225298
docker linux amd64
build-ubuntu-16_04-amd64

00:01:03