Format ESP.getChipId as an 8 character hex instead of 7 digit decimal

[don-willingham]

Copy of arendst/Sonoff-MQTT-OTA-Arduino#289

I have two sonoff duals with chip id's of 15163478 and 15165864. Adding an eighth would work for now, but 10 should be required. Although unlikely, it's possible for UUID collisions. I have two, but as some people have greater numbers of devices, and likely purchased in batches, it's plausible the issue will come up.

ESP.getChipId() returns a 32 bit integer, which can range up to 2,147,483,647. That would require 10 decimal digits. When I was experimenting with simply adding 1 to the UUID for the second channel on a dual, the UUID for both channels would match. They didn't differ as the least significant digit(s) were truncated. My https://github.com/don-willingham/Sonoff-MQTT-OTA-Arduino/tree/dual-wemo branch appends another digit for channel number to the UUID's.

[arendst]

Don did you check the result (8 hex digits). I ask as I failed to get all 8 digits once tried the same.

If so I will implement.

[don-willingham]

Here's a test...

1. Flashed 3.9.10 to ESP-01
2. Enabled WeMo emulation
3. Browsed to /setup.xml URL, and it contains 201612K1292396
4. Browsed to /in URL, and it contains ESP Chip id 1292396, oops, 7 digits, unlike the 8 of my sonoff.
5. Replaced ESP.getChipId() in xdrv_wemohue.ino with 15163478 from one of my sonoffs.
6. Browsed to /setup.xml again, and it contains 201612K1516347, which is missing the 8.
7. Updated to this patch, replaced ESP.getChipId() with 15163478, and now its 201612K00E76056
8. Google search "15163478 to hex" and it returns 0xE76056; but that's not padding with zeros, and we don't need the 0x,

So it will depend on what ESP.getChipId() returns for each sonoff/esp-whatever. Since it's a 32 bit integer.