Fix/enhance: OPTA socket delay and increasing limits.

[ppp-one]

This pull request focuses on fixing readSocket() 100ms delay by removing an unnecessary wait call, and increasing the socket limits from 4 to 8 for the OPTA variant of the ArduinoCore-mbed. The 8 socket limit was chosen to fit my application, and my test Opta has tolerated the increase.

This request targets issues #1067 and #1078.

I only adjusted libraries/SocketWrapper/src/MbedClient.cpp and variants/OPTA/conf/mbed_app.json, the rest seem to be auto-generated from the compiling.

Please let me know if anything needs adjusting.

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