Add and use CNetAddr::HasCJDNSPrefix() helper

src/net.cpp

@@ -275,7 +275,7 @@ std::optional<CService> GetLocalAddrForPeer(CNode& node)
 CService MaybeFlipIPv6toCJDNS(const CService& service)
 {
     CService ret{service};
-    if (ret.m_net == NET_IPV6 && ret.m_addr[0] == 0xfc && IsReachable(NET_CJDNS)) {
+    if (ret.m_net == NET_IPV6 && ret.HasCJDNSPrefix() && IsReachable(NET_CJDNS)) {
         ret.m_net = NET_CJDNS;
     }
     return ret;

src/netaddress.cpp

@@ -450,8 +450,7 @@ bool CNetAddr::IsValid() const
         return false;
     }
 
-    // CJDNS addresses always start with 0xfc
-    if (IsCJDNS() && (m_addr[0] != 0xFC)) {
+    if (IsCJDNS() && !HasCJDNSPrefix()) {
         return false;
     }
 

src/netaddress.h

@@ -182,6 +182,7 @@ public:
     bool IsTor() const;
     bool IsI2P() const;
     bool IsCJDNS() const;
+    [[nodiscard]] bool HasCJDNSPrefix() const { return m_addr[0] == 0xfc; }
     bool IsLocal() const;
     bool IsRoutable() const;
     bool IsInternal() const;