mbed-os-snippet-UDPSocket prints wrong time

The example shows the usage of an UDP socket, and this works. But finally, the received time (seconds sind 1970) prints the correct date only by sudden.
https://github.com/ARMmbed/mbed-os-snippet-UDPSocket/blob/18ae5c765b96ca5bcfd9c584c7cc776ff3ef0867/main.cpp#L48
There is a typecast from a 4 byte to an 8 byte pointer, this works only when the upper 4 bytes are zero.
This is a fix for this (PRs doesnt seem to be used):

```
time_t now = in_data.secs;
printf("Time = %s", ctime(&now));
```

Start in main.cpp at the linked line 48 and inspect how the received seconds value is passed to ctime. Verify the timestamp conversion and run the UDP socket example to confirm that the printed date is consistently correct.

Written by the indexing model from the issue text.