refactor: add kernel/cs_main.*

Co-authored-by: Anthony Towns <aj@erisian.com.au>

src/node/blockstorage.h

@@ -8,6 +8,7 @@
 #include <attributes.h>
 #include <chain.h>
 #include <fs.h>
+#include <kernel/cs_main.h>
 #include <protocol.h>
 #include <sync.h>
 #include <txdb.h>
@@ -17,8 +18,6 @@
 #include <unordered_map>
 #include <vector>
 
-extern RecursiveMutex cs_main;
-
 class ArgsManager;
 class BlockValidationState;
 class CBlock;