package/network-manager: Add upstream patch to fix CVE-2018-15688

package/network-manager: Add upstream patch to fix CVE-2018-15688

NetworkManager includes some parts of the systemd-networkd code in its
codebase. That can be found at src/systemd/src/libsystemd-networkd.
The DHCP implementation provided by systemd-networkd is used when
NetworkManager is configured to use the internal implementation,
however the default is to use dhclient.

When NetworkManager is configured to use the internal dhcp and an
interface is setup with ipv6.method=auto (which is the default value)
or ipv6.method=dhcp, this flaw can be exploited. When using
ipv6.method=auto, the DHCPv6 client can be automatically started with a
Router Advertisement packet.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>