ttcn3-ggsn-test/fragment.config: add NET_NS, VETH
Build the kernel with NET_NS and VETH, so libgtpnl's qemu tests can
download the kernel and use it.
Related: OS#1952
Related: libgtpnl Ibf75514b866fffb11e90529e4705f126b23d7415
Change-Id: I6e893b64718f853b8595de36c090a1326db34419
