net: uip: Callback is only defined for RIME support

We do not need RIME so commenting out the callback call.

Change-Id: I09cd078a3741c6a8e5f4f8fd6387203e6107f218
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

net/ip/contiki/ipv6/sicslowpan.c

@@ -1315,9 +1315,11 @@ packet_sent(void *ptr, int status, int transmissions)
 {
   uip_ds6_link_neighbor_callback(status, transmissions);
 
+#if NETSTACK_CONF_WITH_RIME
   if(callback != NULL) {
     callback->output_callback(status);
   }
+#endif /* NETSTACK_CONF_WITH_RIME */
   last_tx_status = status;
 }
 /*--------------------------------------------------------------------*/