net: move BanMan to its own files

src/interfaces/node.cpp

@@ -6,6 +6,7 @@
 
 #include <addrdb.h>
 #include <amount.h>
+#include <banman.h>
 #include <chain.h>
 #include <chainparams.h>
 #include <init.h>

src/interfaces/node.h

@@ -18,6 +18,7 @@
 #include <tuple>
 #include <vector>
 
+class BanMan;
 class CCoinControl;
 class CFeeRate;
 class CNodeStats;