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
diff --git a/ripngd/ripngd.c b/ripngd/ripngd.c
index 9deac03..6e32d83 100644
--- a/ripngd/ripngd.c
+++ b/ripngd/ripngd.c
@@ -272,7 +272,10 @@
       /* Incoming packet's multicast hop limit. */
       if (cmsgptr->cmsg_level == IPPROTO_IPV6 &&
 	  cmsgptr->cmsg_type == IPV6_HOPLIMIT)
-	*hoplimit = *((int *) CMSG_DATA (cmsgptr));
+	{
+	  int *phoplimit = (int *) CMSG_DATA (cmsgptr);
+	  *hoplimit = *phoplimit;
+	}
     }
 
   /* Hoplimit check shold be done when destination address is