core, eth: abort snapshot generation on snap sync and resume later

core/rawdb/schema.go

@@ -45,6 +45,9 @@ var (
 	// fastTrieProgressKey tracks the number of trie entries imported during fast sync.
 	fastTrieProgressKey = []byte("TrieSync")
 
+	// snapshotDisabledKey flags that the snapshot should not be maintained due to initial sync.
+	snapshotDisabledKey = []byte("SnapshotDisabled")
+
 	// snapshotRootKey tracks the hash of the last snapshot.
 	snapshotRootKey = []byte("SnapshotRoot")