LimeSuiteNG Legacy API limits TX LMS_SendStream to a sample_count of 65535

Trying to use LMS_SendStream in the LimeSuiteNG legacy API and I have found that it causes a DMA error if the sample_count is set to more than 65535 samples.

The original LimeSuite API worked without error at up to a sample_count of 500000.

This is probably linked to #124 

I can provide more info if required, but the test setup is very similar to #124.

Thanks

Dave