dnstap: avoid a false-positive warning

dnstap: avoid a false-positive warning

../modules/dnstap/dnstap.c: In function 'dnstap_config':
../modules/dnstap/dnstap.c:410:29: warning: 'strndup' specified bound 4096 exceeds source size 17 [-Wstringop-overread]
  410 |                 sock_path = strndup(DEFAULT_SOCK_PATH, PATH_MAX);
      |                             ^
../modules/dnstap/dnstap.c:423:37: warning: 'strndup' specified bound 4096 exceeds source size 17 [-Wstringop-overread]
  423 |                         sock_path = strndup(DEFAULT_SOCK_PATH, PATH_MAX);
      |                                     ^

We don't need to restrict our built-in path defaults to PATH_MAX
characters, as they just can't be that long and it's not an issue if we
shoot over it anyway - opening such a file would only fail.