Fix memory leak in GCM by adding gcm_free()

include/polarssl/gcm.h

@@ -197,6 +197,13 @@ int gcm_finish( gcm_context *ctx,
                 unsigned char *tag,
                 size_t tag_len );
 
+/**
+ * \brief           Free a GCM context and underlying cipher sub-context
+ *
+ * \param ctx
+ */
+void gcm_free( gcm_context *ctx );
+
 /**
  * \brief          Checkup routine
  *