Add back n_slots to RamBuffer

In tests you don't want it to consume all your ram.

core-buffer/include/RamBuffer.hpp

@@ -8,6 +8,7 @@ class RamBuffer {
     const std::string detector_name_;
     const int n_modules_;
     const int module_n_;
+    const int n_slots_;
 
     const size_t meta_size_;
     const size_t image_size_;
@@ -22,7 +23,8 @@ class RamBuffer {
 public:
     RamBuffer(const std::string& detector_name,
               const int n_modules,
-              const int module_n=0);
+              const int module_n=0,
+              const int n_slots=RAM_BUFFER_N_SLOTS);
     ~RamBuffer();
 
     void write_frame(const ModuleFrame *src_meta, const char *src_data) const;