[sim70x0] Clean up socket receive

[tpecar-ltek]

If I understand the AWS stack correctly, the higher-level libraries (eg. coreMQTT, or the underlying TLS / SSL encryption layers) interface to sockets via the TCP_Sockets interface, which is provided by wrappers to the actual implementation, which can either be

• the FreeRTOS TCP (providing TCP/IP stack on MCU) or
• the FreeRTOS Cellular Interface (reusing the TCP/IP stack on modem)

Current implementations are available here

The FreeRTOS Cellular TCP_Sockets wrapper provides modem-agnostic blocking receive (handled via event groups and data ready callbacks), thereby allowing the modem implementation only needing to support the non-blocking receive (possibly returning less than the requested number of bytes). The Cellular_SocketRecv() API seems to imply such operation. Some ports (eg. BG96) follow this.

The current sim70x0 implementation has implemented a blocking receive via pSimContext->pdnEvent event group, which is then manipulated in the URC handler and various parser functions.

This can probably be removed without effect on the higher layers, simplifying the port.

[chinglee-iot]

@tpecar-ltek
Sorry for late reply. This port is contributed by community. Are you able to create a PR to update the implementation?