A potential bug in NNG UDP transport noted

[JaylinYu]

Test udp duplicate bind:
  udp_test.c:293: Check nni_init() succeeds... ok
  udp_test.c:294: Check nni_plat_udp_open(&u1, &sa) succeeds... ok
  udp_test.c:295: Check nni_plat_udp_sockname(u1, &sa) succeeds... ok
  udp_test.c:296: Check nni_plat_udp_open(&u2, &sa) fails with Address in use... ok
  SUCCESS: All conditions have passed.
  Duration: 0.000150 secs

Test udp send v6 from v4:
panic: pthread_mutex_lock: Invalid argument
This message is indicative of a BUG.
Report this at https://github.com/emqx/nanomq
1   udp_test                            0x00000001044f9fa0 nni_panic + 164
2   udp_test                            0x0000000104510d44 nni_pthread_mutex_lock + 72
3   udp_test                            0x0000000104510cf0 nni_plat_mtx_lock + 24
4   udp_test                            0x00000001045045e0 nni_mtx_lock + 24
5   udp_test                            0x0000000104511dc8 nni_plat_udp_send + 60
6   udp_test                            0x00000001044e8460 test_udp_send_v6_from_v4 + 588
7   udp_test                            0x00000001044e8f20 test_do_run_ + 244
8   udp_test                            0x00000001044e57b0 test_run_ + 276
9   udp_test                            0x00000001044e43ec main + 760
10  dyld                                0x000000018fc1a0e0 start + 2360
  udp_test.c:316: Check nni_init() succeeds... ok
  udp_test.c:317: Check nng_aio_alloc(&aio1, NULL, NULL) succeeds... ok
  udp_test.c:318: Check nni_plat_udp_open(&u1, &sa) succeeds... failed
    nni_plat_udp_open(&u1, &sa): expected success, got Permission denied (16)
  ERROR: Test interrupted by SIGABRT.

Summary:
  Count of all unit tests:        7
  Count of run unit tests:        7
  Count of failed unit tests:     1
  Count of skipped unit tests:    0
FAILED: 1 of 7 unit tests has failed.