xl2tpd: Close calls when underlying pppd terminate.

Unsure the cause, but we found that upon ppp terminating xl2tpd would
only reap the PID, but not actually close the inner call, then at a
later stage would issue a kill() for that PID.

In our environment with high call turnover this would eventually result
in xl2tpd kill()'ing other critical services like mariadb and/or
syslog-ng which would upon reloads and rotations have a tendency to
re-use PIDs that were previously used by pppd processes.

We also believe that this should sort out the problem where IPs wouldn't
get cycled and re-used.

Closes: xelerance#252
Closes: xelerance#255
Signed-off-by: Jaco Kroon <[email protected]>

xl2tpd.c

@@ -257,6 +257,9 @@ static void child_handler (int sig)
             {
                 if (c->pppd == pid)
                 {
+                    /* pid is no longer valid, avoid killing it later by accident in destroy_call() */
+                    c->pppd = 0;
+
                     if ( WIFEXITED( status ) )
                     {
                         l2tp_log (LOG_DEBUG, "%s : pppd exited for call %d with code %d\n", __FUNCTION__,
@@ -283,6 +286,8 @@ static void child_handler (int sig)
 #endif
                     close (c->fd);
 #ifdef USE_KERNEL
+                 } else {
+                     call_close (c);
                  }
 #endif
                     c->fd = -1;