ripngd: compiler warnings cleanup

* ripngd/ripng_interface.c
  * ripng_check_max_mtu(): unused, sayonara
  * ripng_interface_down(): cast flag arguments to logging function
  * ripng_interface_add(): idem
  * ripng_interface_delete(): idem
* ripngd/ripngd.c
  * ripng_recv_packet(): avoid aliasing warning dereferencing pointer
2 files changed