Example Applications - Bug fixes and enhancements for tx_waveforms and tx_samples_from_file

[joelkeeling]

Pull Request Details

Description

• Fixed bug in channel handling in tx_waveforms so now all available channels can be used
• Fixed bug in channel handling in tx_samples_from_file so now all available channels can be used
• Added support for the 'power' argument in tx_samples_from_file so that it matched other example applications
• Added support for multiple channels with the 'channels' argument in tx_samples_from_file so that it matched other example applications

Related Issues

Fixes #705
Fixes #706

Testing Done

This should not affect the core UHD library as these changes only apply to the example applications.
Re-ran both examples applications multiple times on a hardware setup that included an X410 and SC2430 SCM. Tested all input arguments that were added or modified.

Checklist

• I have read the CONTRIBUTING document.
• My code follows the code style of this project. See CODING.md.
• (Not applicable) I have updated the documentation accordingly.
• (Not applicable) I have added tests to cover my changes, and all previous tests pass.
• (Not applicable) I have checked all compat numbers if they need updating (FPGA compat,
  MPM compat, noc_shell, specific RFNoC block, ...)

[github-actions]

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[joelkeeling]

I have read the CLA Document and I hereby sign the CLA

[joelkeeling]

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