radioInterface: Reset sample buffer cursors on each start

Non-zero buffer indices may lead to uplink/downlink timing offset
during repeated start/stop cycles. Mainly affects USRP2 and other
resampled devices that rely on the buffer to absorb sample block
sizes that are not multiples of the burst size.

Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
diff --git a/Transceiver52M/radioInterface.cpp b/Transceiver52M/radioInterface.cpp
index 369f2ac..14a4fc2 100644
--- a/Transceiver52M/radioInterface.cpp
+++ b/Transceiver52M/radioInterface.cpp
@@ -185,6 +185,9 @@
   if (!mRadio->start())
     return false;
 
+  recvCursor = 0;
+  sendCursor = 0;
+
   writeTimestamp = mRadio->initialWriteTimestamp();
   readTimestamp = mRadio->initialReadTimestamp();