ripngd: Add missing systemd notifications

Initial pass of adding systemd callbacks were missed for
ripngd.  This commit adds those calls.

Ticket: CM-9267
Reviewed-by: Don Slice
Testing: See Bug

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

ripngd/ripng_main.c

@@ -155,6 +155,7 @@ sigint (void)
   if (! retain_mode)
     ripng_clean ();
 
+  systemd_send_stopping ();
   exit (0);
 }
 
@@ -299,6 +300,8 @@ main (int argc, char **argv)
       exit (1);
     }
 
+  systemd_send_started (master);
+
   /* Create VTY socket */
   vty_serv_sock (vty_addr, vty_port, RIPNG_VTYSH_PATH);