Add the flag for disabling IPv6 checks

Host operating system: output of uname -a

Linux monitor 4.13.4-gentoo #1 SMP Thu Oct 5 16:11:49 MSK 2017 x86_64 Intel(R) Xeon(R) CPU 5160 @ 3.00GHz GenuineIntel GNU/Linux

node_exporter version: output of node_exporter --version

node_exporter, version 0.15.0 (branch: , revision: 6e2053c)
build user: portage@monitor
build date: 20171105-14:36:29
go version: go1.9.1

node_exporter command line flags

command_args="--collector.textfile.directory=/var/lib/node_exporter/
--web.listen-address localhost:19080
--no-collector.zfs
--no-collector.wifi
--no-collector.mdadm
--no-collector.infiniband
--log.level=debug"

Are you running node_exporter in Docker?

no

What did you do that produced an error?

In the OS kernel, IPv6 is disabled

What did you expect to see?

The work of the netstat module

What did you see instead?

time="2017-11-06T13:23:45+03:00" level=error msg="ERROR: netstat collector failed after 0.000344s: couldn't get SNMP6 stats: open /proc/net/snmp6: no such file or directory" source="collector.go:123"

[SuperQ]

Yes, that should be a soft error. We should also soft-error for ipv4 stats so that people with ipv6-only don't get errors too. 😄

[SuperQ]

Ahh, that was fixed by #718

This is a duplicate of #717

thx