CVE-2018-15688,network-manager: Jessie is not affected

The vulnerable code does not exist in this version. The systemd files were
imported for the first time in April 2015.

https://cgit.freedesktop.org/NetworkManager/NetworkManager/commit/src/systemd/src/libsystemd-network/dhcp6-option.c?id=8af18182f3bf55270aadc83f32c518935d553a2a