Import USRP support.

Add LO offset support.
Only set tx/rx_bandwidth after getting tx stream, to reduce TX LO leakage for <10MHz bandwidths.
Check for reference and LO lock before getting streams.

plugins/samplesource/usrpinput/usrpinputsettings.cpp

@@ -28,10 +28,11 @@ void USRPInputSettings::resetToDefaults()
 {
     m_centerFrequency = 435000*1000;
     m_devSampleRate = 3000000;
+    m_loOffset = 0;
     m_dcBlock = false;
     m_iqCorrection = false;
     m_log2SoftDecim = 0;
-    m_lpfBW = 5.5e6f;
+    m_lpfBW = 10e6f;
     m_gain = 50;
     m_antennaPath = "TX/RX";
     m_gainMode = GAIN_AUTO;
@@ -63,6 +64,7 @@ QByteArray USRPInputSettings::serialize() const
     s.writeString(13, m_reverseAPIAddress);
     s.writeU32(14, m_reverseAPIPort);
     s.writeU32(15, m_reverseAPIDeviceIndex);
+    s.writeS32(16, m_loOffset);
     return s.final();
 }
 
@@ -105,6 +107,7 @@ bool USRPInputSettings::deserialize(const QByteArray& data)
 
         d.readU32(15, &uintval, 0);
         m_reverseAPIDeviceIndex = uintval > 99 ? 99 : uintval;
+        d.readS32(16, &m_loOffset, 0);
 
         return true;
     }