kernel: Move default cache constants to caches

They are not related to the txdb, so a better place for them is the
new kernel and node cache file. Re-use the default amount of kernel
cache for the default node cache.

src/node/caches.cpp

@@ -7,7 +7,6 @@
 #include <common/args.h>
 #include <index/txindex.h>
 #include <kernel/caches.h>
-#include <txdb.h>
 
 #include <algorithm>
 #include <string>
@@ -22,8 +21,8 @@ static constexpr int64_t MAX_FILTER_INDEX_CACHE{1024};
 namespace node {
 CacheSizes CalculateCacheSizes(const ArgsManager& args, size_t n_indexes)
 {
-    int64_t nTotalCache = (args.GetIntArg("-dbcache", nDefaultDbCache) << 20);
-    nTotalCache = std::max(nTotalCache, nMinDbCache << 20); // total cache cannot be less than nMinDbCache
+    int64_t nTotalCache = (args.GetIntArg("-dbcache", DEFAULT_DB_CACHE) << 20);
+    nTotalCache = std::max(nTotalCache, MIN_DB_CACHE << 20);
     IndexCacheSizes sizes;
     sizes.tx_index = std::min(nTotalCache / 8, args.GetBoolArg("-txindex", DEFAULT_TXINDEX) ? MAX_TX_INDEX_CACHE << 20 : 0);
     nTotalCache -= sizes.tx_index;

src/node/caches.h

@@ -11,6 +11,11 @@
 
 class ArgsManager;
 
+//! min. -dbcache (MiB)
+static constexpr int64_t MIN_DB_CACHE{4};
+//! -dbcache default (MiB)
+static constexpr int64_t DEFAULT_DB_CACHE{DEFAULT_KERNEL_CACHE};
+
 namespace node {
 struct IndexCacheSizes {
     size_t tx_index{0};