gnrc: ndp: suppress wrong cppcheck warnings

sys/net/gnrc/network_layer/ndp/gnrc_ndp.c

@@ -672,6 +672,8 @@ void gnrc_ndp_retrans_nbr_sol(gnrc_ipv6_nc_t *nc_entry)
                 mutex_unlock(&ipv6_iface->mutex);
             }
         }
+        /* cppcheck-suppress knownConditionTrueFalse
+         * cppcheck bug: probes_remaining is initialized to a value > 1 */
         else if (nc_entry->probes_remaining <= 1) {
 
             /* For a 6LoWPAN router entries may be set to UNREACHABLE instead

sys/net/gnrc/network_layer/ndp/node/gnrc_ndp_node.c

@@ -80,6 +80,8 @@ kernel_pid_t gnrc_ndp_node_next_hop_l2addr(uint8_t *l2addr, uint8_t *l2addr_len,
     }
 #endif
 
+    /* cppcheck-suppress knownConditionTrueFalse
+     * cppcheck bug: next_hop_ip might be initialized if a FIB is available */
     if (next_hop_ip == NULL) {            /* no route to host */
         if (!dst_link_local) {
             if (iface == KERNEL_PID_UNDEF) {