Fix _Cellular_AtcmdDataSend interDelayMS

[chinglee-iot]

Fix the inter delay for _Cellular_AtcmdDataSend

Description

interDelayMS is designed to adapt the behavior of cellular modem that a minimum delay is required before sending data.

For example, after the @ prompt reception, SARA-R4 AT command +USOWR requires the cellular library to wait for a minimum 50ms before sending data.

The delay should happen after data send command success but before sending data. This PR fix the interDelayMS.

• Move the delay to code between the data send command success and sending data.

Test Steps

Running SARA-R4 demo without problem.

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

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