Babel: Parse flags in Hello TLV

RFC6126bis introduces a flags field for the Hello TLV, and adds a unicast flag
that is used to signify that a hello was sent as unicast. This adds parsing of
the flags field and ignores such unicast hellos, which preserves compatibility
until we can add a proper implementation of the unicast hello mechanism.

Thanks to Toke Hoiland-Jorgensen for the patch.
49 jobs from master in 11 minutes and 32 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Image
passed #79877
dind allowed to fail
docker_centos-6-amd64

00:00:25

passed #79878
dind allowed to fail
docker_centos-7-amd64

00:00:33

passed #79867
dind allowed to fail
docker_debian-7-amd64

00:00:28

passed #79871
dind allowed to fail
docker_debian-7-i386

00:00:24

passed #79868
dind allowed to fail
docker_debian-8-amd64

00:00:26

passed #79872
dind allowed to fail
docker_debian-8-i386

00:00:25

passed #79869
dind allowed to fail
docker_debian-9-amd64

00:00:27

passed #79873
dind allowed to fail
docker_debian-9-i386

00:00:31

passed #79870
dind allowed to fail
docker_debian-testing-amd64

00:00:27

passed #79874
dind allowed to fail
docker_debian-testing-i386

00:00:31

passed #79875
dind allowed to fail
docker_fedora-25-amd64

00:00:30

passed #79876
dind allowed to fail
docker_fedora-26-amd64

00:00:33

passed #79879
dind allowed to fail
docker_opensuse-42_3-amd64

00:00:25

passed #79880
dind allowed to fail
docker_ubuntu-14_04-amd64

00:02:49

passed #79881
dind allowed to fail
docker_ubuntu-16_04-amd64

00:01:54

 
  Build
passed #79894
docker linux amd64
build-centos-6-amd64

00:01:08

passed #79895
docker linux amd64
build-centos-6-amd64-v6

00:01:08

passed #79896
docker linux amd64
build-centos-7-amd64

00:01:05

passed #79897
docker linux amd64
build-centos-7-amd64-v6

00:01:07

passed #79882
docker linux amd64
build-debian-7-amd64

00:01:03

passed #79886
docker linux amd64
build-debian-7-amd64-v6

00:01:06

passed #79904
docker linux amd64
build-debian-7-i386

00:00:38

passed #79905
docker linux amd64
build-debian-7-i386-v6

00:00:40

passed #79883
docker linux amd64
build-debian-8-amd64

00:01:08

passed #79887
docker linux amd64
build-debian-8-amd64-v6

00:01:26

passed #79906
docker linux amd64
build-debian-8-i386

00:00:57

passed #79907
docker linux amd64
build-debian-8-i386-v6

00:00:58

passed #79884
docker linux amd64
build-debian-9-amd64

00:01:35

passed #79888
docker linux amd64
build-debian-9-amd64-v6

00:01:12

passed #79908
docker linux amd64
build-debian-9-i386

00:00:58

passed #79909
docker linux amd64
build-debian-9-i386-v6

00:00:45

passed #79885
docker linux amd64
build-debian-testing-amd64

00:01:10

passed #79889
docker linux amd64
build-debian-testing-amd64-v6

00:01:36

passed #79910
docker linux amd64
build-debian-testing-i386

00:00:48

passed #79911
docker linux amd64
build-debian-testing-i386-v6

00:00:51

passed #79890
docker linux amd64
build-fedora-25-amd64

00:01:11

passed #79891
docker linux amd64
build-fedora-25-amd64-v6

00:01:32

passed #79892
docker linux amd64
build-fedora-26-amd64

00:01:10

passed #79893
docker linux amd64
build-fedora-26-amd64-v6

00:01:23

passed #79912
freebsd amd64
build-freebsd-11-amd64

00:07:25

passed #79913
freebsd amd64
build-freebsd-11-amd64-v6

00:07:40

passed #79914
freebsd i386
build-freebsd-11-i386

00:07:24

passed #79915
freebsd i386
build-freebsd-i386-v6

00:07:12

passed #79898
docker linux amd64
build-opensuse-42_3-amd64

00:00:59

passed #79899
docker linux amd64
build-opensuse-42_3-amd64-v6

00:01:10

passed #79900
docker linux amd64
build-ubuntu-14_04-amd64

00:01:05

passed #79901
docker linux amd64
build-ubuntu-14_04-amd64-v6

00:01:09

passed #79902
docker linux amd64
build-ubuntu-16_04-amd64

00:00:39

passed #79903
docker linux amd64
build-ubuntu-16_04-amd64-v6

00:00:32