[2.2] rsyslog is flooded with "no link-local IPv6 address for $IFACE" for link-down interfaces

[Mike Pontillo]

rsyslog reports the following, many times per second, for interfaces which are link-down:

Mar 28 23:05:07 skylake dhclient[22640]: no link-local IPv6 address for eno1
Mar 28 23:05:07 skylake dhclient[22640]:
Mar 28 23:05:07 skylake dhclient[22640]: If you think you have received this message due to a bug rather
Mar 28 23:05:07 skylake dhclient[22640]: than a configuration issue please read the section on submitting
Mar 28 23:05:07 skylake dhclient[22640]: bugs on either our web page at www.isc.org or in the README file
Mar 28 23:05:07 skylake dhclient[22640]: before submitting a bug. These pages explain the proper
Mar 28 23:05:07 skylake dhclient[22640]: process and the information we find helpful for debugging..
Mar 28 23:05:07 skylake dhclient[22640]:
Mar 28 23:05:07 skylake dhclient[22640]: exiting.

$ ip link show dev eno1
3: eno1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 0c:c4:7a:c0:31:fa brd ff:ff:ff:ff:ff:ff

$ ip addr list dev eno1
3: eno1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 0c:c4:7a:c0:31:fa brd ff:ff:ff:ff:ff:ff

Notice the link is NO-CARRIER.

It seems like we should avoid starting the DHCP client if the link's NO-CARRIER bit is set.

See also: bug #1640147.