device: do not set disable_ipv6 on external
Summary
For device connecting via external connection, NM still toggles the
disable_ipv6
sysctl setting into 0 even if systemd-sysctl
sets it
nto 1. To fix it, NM should not touch the IPv6 setting when device's
sys_iface_state is external.
Purpose
Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2207878.
Checklist
Please read https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/main/CONTRIBUTING.md before opening the merge request. In particular, check that:
-
the subject for all commits is concise and explicative -
the message for all commits explains the reason for the change -
the source is properly formatted -
any relevant documentation is up to date -
you have added unit tests if applicable