core: support creating ip6-config setting with disabled method

Create the new setting with method=disabled if IPv6 is disabled in the
sysctl.
14 jobs for bg/ipv6-disabled in 30 minutes and 55 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #338717
allowed to fail
checkpatch

00:01:26

manual #338722
allowed to fail manual
t_centos:7.5.1804
passed #338723
t_centos:7.6.1810

00:22:30

passed #338726
t_debian:9

00:12:59

passed #338728
t_debian:sid

00:18:19

manual #338727
allowed to fail manual
t_debian:testing
passed #338718
t_fedora:28

00:28:54

passed #338719
t_fedora:29

00:30:55

failed #338720
t_fedora:30

00:08:15

manual #338721
allowed to fail manual
t_fedora:rawhide
passed #338724
t_ubuntu:16.04

00:17:30

passed #338725
t_ubuntu:18.04

00:18:28

 
  External
failed NetworkManager test verification

failed NetworkManager test verification

05:23:18

 
Name Stage Failure
failed
t_fedora:30 Test
./src/platform/tests/test-link-linux.valgrind-log:   fun:main
./src/platform/tests/test-link-linux.valgrind-log:}
+ echo '>>>> PRINT VALGRIND LOGS (valgrind test) (done)'
+ die 'valgrind test failed'
>>>> PRINT VALGRIND LOGS (valgrind test) (done)
valgrind test failed
+ printf '%s\n' 'valgrind test failed'
+ exit 1
ERROR: Job failed: exit code 1