[net/refactor] Add connection type as a member var to CNode

- Directly maintaining the connection type prevents having to deduce it from
  several flags.

src/net.cpp

@@ -2749,6 +2749,7 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
     // traffic).
     id(idIn),
     nLocalHostNonce(nLocalHostNonceIn),
+    m_conn_type(conn_type_in),
     nLocalServices(nLocalServicesIn),
     nMyStartingHeight(nMyStartingHeightIn)
 {

src/net.h

@@ -875,6 +875,7 @@ public:
 private:
     const NodeId id;
     const uint64_t nLocalHostNonce;
+    const ConnectionType m_conn_type;
 
     //! Services offered to this peer.
     //!