[netgroupman] Move asmap checksum calculation to NetGroupManager

src/netgroup.cpp

@@ -4,8 +4,16 @@
 
 #include <netgroup.h>
 
+#include <hash.h>
 #include <util/asmap.h>
 
+uint256 NetGroupManager::GetAsmapChecksum() const
+{
+    if (!m_asmap.size()) return {};
+
+    return SerializeHash(m_asmap);
+}
+
 std::vector<unsigned char> NetGroupManager::GetGroup(const CNetAddr& address) const
 {
     std::vector<unsigned char> vchRet;