LMSDevice: Fix initial timestamp offset of 2500

ts_initial must not point to the timestamp of the first sample
in the last "flush" sample buffer, but to the first timestamp we
expect in the next buffer.

Change-Id: I23af62870544d4c6cf5f6e2d6578936603bceb91

Transceiver52M/device/lms/LMSDevice.cpp

@@ -345,7 +345,7 @@ bool LMSDevice::flush_recv(size_t num_pkts)
 			return false;
 		}
 
-		ts_initial = rx_metadata.timestamp;
+		ts_initial = rx_metadata.timestamp + len;
 	}
 
 	LOG(INFO) << "Initial timestamp " << ts_initial << std::endl;