Limited relaying/storing of foreign addresses

Introduce a boolean variable for each "network" (ipv4, ipv6, tor, i2p),
and track whether we are likely to able to connect to it. Addresses in
"addr" messages outside of our network get limited relaying and are not
stored in addrman.

src/netbase.h

@@ -17,6 +17,19 @@ extern int nConnectTimeout;
 #undef SetPort
 #endif
 
+enum Network
+{
+    NET_UNROUTABLE,
+    NET_IPV4,
+    NET_IPV6,
+    NET_TOR,
+    NET_I2P,
+
+    NET_MAX
+};
+
+enum Network ParseNetwork(std::string net);
+
 /** IP address (IPv6, or IPv4 using mapped IPv6 range (::FFFF:0:0/96)) */
 class CNetAddr
 {
@@ -48,6 +61,7 @@ class CNetAddr
         bool IsRoutable() const;
         bool IsValid() const;
         bool IsMulticast() const;
+        enum Network GetNetwork() const;
         std::string ToString() const;
         std::string ToStringIP() const;
         int GetByte(int n) const;