Make the destructor of EstimatorInterface virtual

* This is a sane choice (and should arguably always be done for classes with
  virtual methods to avoid undefined behavior)
* It is required for wrapping the EstimatorInterface with SWIG (without virtual
  destructor, deriving from the EstimatorInterface leads to
  -Werror=delete-non-virtual-dtor).

EKF/estimator_interface.h

@@ -52,7 +52,7 @@ class EstimatorInterface
 
 public:
 	EstimatorInterface() = default;
-	~EstimatorInterface() = default;
+	virtual ~EstimatorInterface() = default;
 
 	virtual bool init(uint64_t timestamp) = 0;
 	virtual bool update() = 0;