Increase MAX_PAYLOAD_SIZE to 512 bytes

[santaimpersonator]

Changes:
Update MAX_PAYLOAD_SIZE from 276 to 512 to support getModuleInfo() on the ZED-X20P GNSS module, which requires at least 288 bytes.

I verified this modification with an ESP32 Thing Plus and the ZED-X20P breakout.

SparkFun u-blox Example
FWVER: 2.0
Firmware: HPG
PROTVER: 50.2
MOD: ZED-X20P

Resolves:
When utilizing Basics > Example8_GetModuleInfo with the ZED-X20P, the library appears to run into a buffer overflow before it can detect the end of the response payload.

Debug Message:

Sending: CLS:MON ID:0x4 Len: 0x0 Payload:
sendCommand: Waiting for No ACK response3
checkUbloxI2C: 288 bytes available
processUBX: counter hit maximum_payload_size + 6! activePacketBuffer: 0 maximum_payload_size: 276
waitForNoACKResponse: TIMEOUT after 1100 msec. No packet received.

[PaulZC]

Thanks Wes (@santaimpersonator ),

I can't replicate this. The X20P I have returns 250 bytes. It doesn't include the "MOD=" extension. Your firmware must be slightly different, and does include the "MOD=", taking the payload length to 280 bytes. (Each extension is 30 bytes.)

But it's clear we need to increase. RAM is still precious on some platforms, so I think we should go with 300, not 512...

Cheers!
Paul