include issue in src/base/ServiceBase.h

I provide a fix for `firewall` service, just to keep track.
The issue could be generalized to other services.

`src/base/FirewallBase.h`
```
-#include "../Chain.h"
-#include "../SessionTable.h"

+class Chain;
+class SessionTable;
```

`src/base/FirewallBase.cpp`
```
+#include "../Chain.h"
+#include "../SessionTable.h"
```