[minip] fix warning in new changes
Building with -Werror locally.
@@ -148,7 +148,7 @@ status_t udp_send_iovec(const iovec_t *iov, uint iov_count, udp_socket_t *handle
udp->chksum = rfc768_chksum(ip, udp);
#endif
- LTRACEF("packet paylod len %zu\n", len);
+ LTRACEF("packet paylod len %ld\n", len);
minip_tx_handler(p);
