banman: create and split out banman

Some say he has always been.

src/test/test_bitcoin_main.cpp

@@ -11,6 +11,7 @@
 #include <boost/test/unit_test.hpp>
 
 std::unique_ptr<CConnman> g_connman;
+std::unique_ptr<BanMan> g_banman;
 
 [[noreturn]] void Shutdown(void* parg)
 {