Attempt best-match sample rate near "default"

- Fix hard-coded usage of DEFAULT_SAMPLE_RATE, now “suggested” rate

src/sdr/SDRDeviceInfo.cpp

@@ -1,4 +1,5 @@
 #include "SDRDeviceInfo.h"
+#include <cstdlib>
 
 SDRDeviceRange::SDRDeviceRange() {
     low = 0;
@@ -84,6 +85,20 @@ std::vector<long> &SDRDeviceChannel::getSampleRates() {
     return sampleRates;
 }
 
+long SDRDeviceChannel::getSampleRateNear(long sampleRate_in) {
+    long returnRate = sampleRates[0];
+    long sDelta = (long)sampleRate_in-sampleRates[0];
+    long minDelta = abs(sDelta);
+    for (std::vector<long>::iterator i = sampleRates.begin(); i != sampleRates.end(); i++) {
+        long thisDelta = abs(sampleRate_in - (*i));
+        if (thisDelta < minDelta) {
+            minDelta = thisDelta;
+            returnRate = (*i);
+        }
+    }
+    return returnRate;
+}
+
 std::vector<long long> &SDRDeviceChannel::getFilterBandwidths() {
     return filterBandwidths;
 }

src/sdr/SDRDeviceInfo.h

@@ -69,6 +69,7 @@ public:
     SDRDeviceRange &getRFRange();
 
     std::vector<long> &getSampleRates();
+    long getSampleRateNear(long sampleRate_in);
     std::vector<long long> &getFilterBandwidths();
     
     const bool& hasHardwareDC() const;

src/sdr/SoapySDRThread.cpp

@@ -11,7 +11,7 @@ SDRThread::SDRThread() : IOThread() {
     deviceConfig.store(NULL);
     deviceInfo.store(NULL);
 
-    sampleRate.store(DEFAULT_SAMPLE_RATE);
+    sampleRate.store(0);
     frequency.store(0);
     offset.store(0);
     ppm.store(0);

src/sdr/SoapySDRThread.h

@@ -22,7 +22,7 @@ public:
     std::vector<liquid_float_complex> data;
 
     SDRThreadIQData() :
-            frequency(0), sampleRate(DEFAULT_SAMPLE_RATE), dcCorrected(true), numChannels(0) {
+            frequency(0), sampleRate(0), dcCorrected(true), numChannels(0) {
 
     }