xl2tpd: refactor for more resilience.

xl2tpd: refactor for more resilience.

 - Use netifd no_proto_task for notifying that xl2tpd does not have a
   protocol task running.
 - Use procd for xl2tpd service management.
 - Refreshed 2xx patches to

    - Prevent leftover regular type control result file.
    - Allow xl2tpd run as foreground process while logging via syslog.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
 - bumped version
 - removed dependency on `ip` package as routes are setup by netifd
   if iproute2 is actually required, please depend on
   `@(PACKAGE_ip||PACKAGE_ip-full)` instead of `ip`

Signed-off-by: Daniel Golle <daniel@makrotopia.org>