dnsmasq: update to 2.68

Fixes a bug with libvirt and DHCP, which is fixed in 2.66.

"Handle the situation where libc headers define
SO_REUSEPORT, but the kernel in use doesn't, to cope with
the introduction of this option to Linux. Thanks to Rich
Felker for the bug report."

Signed-off-by: Christian Ziethén <Christian.Ziethen@enea.com>
Signed-off-by: Joe MacDonald <joe@deserted.net>