improve SourceVITA49 to support detection of AGC/MGC toggling

[James-Wang-JM]

Testing with a device which is a VITA49 transmitter. Configure the device to transmit a VITA49 stream which conveys short IQ data.

Launch component SourceVITA49 in sandbox and configure it to receive the VITA49 stream, display SRI of dataShort_out port, monitor AUTO_GAIN_CONTROL value. The value is always true, even after change the AGC/MGC setting to MGC on VITA49 transmitter.

The following code snippet from function SourceVITA49_i::process_context() in SourceVITA49.cpp shows

1. it treats both _TRUE and _FALSE as AGC enabled.
2. it doesn't support detection of AGC/MGC toggling

    if (!isNull(contextPacket_g->isAutomaticGainControl()) && contextPacket_g->isAutomaticGainControl() == _TRUE) {
        addModifyKeyword<bool>(&outputSRI, "AUTO_GAIN_CONTROL", true);
        LOG_DEBUG(SourceVITA49_i, "AUTO_GAIN_CONTROL: " << true);
    }

[RedhawkDeployer]

We have confirmed the issue and have put the issue on our backlog for scheduling.