Draft: add xl2tpd runscript

2024-10-25_21:37:58.41279 invoke-run: Starting xl2tpd...
2024-10-25_21:37:58.42282 xl2tpd[29447]: Not looking for kernel SAref support.
2024-10-25_21:37:58.42285 xl2tpd[29447]: Using l2tp kernel support.
...
24: ppp-aaisp-l2tp: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1460 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 3
    link/ppp
...
      |          `-runsv-+-svlogd
      |                  `-xl2tpd---pppd

Start and stop work. Restart fails initially but then succeeds. There is some syncronisation issue with pppd but this also occurs with the initscripts so this is not a regression. Scope for future enhancement to improve the shutdown side to sync with the removal of the ppp link.