ndp: pass size to fib_get_next_hop as a pointer

sys/net/network_layer/ng_ndp/ng_ndp.c

@@ -434,14 +434,14 @@ kernel_pid_t ng_ndp_next_hop_l2addr(uint8_t *l2addr, uint8_t *l2addr_len,
     next_hop_ip = ng_ipv6_ext_rh_next_hop(hdr);
 #endif
 #ifdef MODULE_FIB
-    size_t next_hop_size;
+    size_t next_hop_size = sizeof(ng_ipv6_addr_t);
     uint32_t next_hop_flags = 0;
     ng_ipv6_addr_t next_hop_actual; /* FIB copies address into this variable */
 
     if ((next_hop_ip == NULL) &&
         (fib_get_next_hop(&iface, next_hop_actual.u8, &next_hop_size,
                           &next_hop_flags, (uint8_t *)dst,
-                          sizeof(ng_ipv6_addr_t), 0) >= 0) &&
+                          &next_hop_size, 0) >= 0) &&
         (next_hop_size == sizeof(ng_ipv6_addr_t))) {
         next_hop_ip = &next_hop_actual;
     }