SSU2: Don't rectify MTUs to mod 16 in SSU2 addresses

Set max MTU for range48.org brokered addresses
Limit MTU for brokered addresses in UDPAddress also

router/java/src/net/i2p/router/transport/udp/MTU.java

@@ -90,12 +90,18 @@ public class MTU {
                                 log.logAlways(Log.WARN, "Unusually low MTU " + mtu + " for interface " + ia +
                                                         ", consider disabling");
                             }
-                            // fix for he.net tunnels with too big MTU
-                            if (isIPv6 && mtu > 1472) {
+                            // fix for brokered tunnels with too big MTU
+                            if (isIPv6 && mtu > 1420) {
                                 byte[] ip = addr.getAddress();
-                                if (ip[0] == 0x20 && ip[1] == 0x01 &&
+                                // he.net
+                                if (mtu > 1472 &&
+                                    ip[0] == 0x20 && ip[1] == 0x01 &&
                                     ip[2] == 0x04 && ip[3] == 0x70)
                                     return 1472;
+                                // route48.org, supports Wireguard
+                                if (ip[0] == 0x2a && ip[1] == 0x06 &&
+                                    ip[2] == (byte) 0xa0 && ip[3] == 0x04)
+                                    return 1420;
                             }
                             if (isSSU2)
                                 return Math.min(mtu, PeerState2.MAX_MTU);

router/java/src/net/i2p/router/transport/udp/UDPAddress.java

@@ -98,12 +98,27 @@ class UDPAddress {
         _isIPv4 = (_host != null && _host.contains(".")) || (caps != null && caps.contains("4"));
         _isIPv6 = (_host != null && _host.contains(":")) || (caps != null && caps.contains("6"));
 
+        final boolean ssu2only = addr.getTransportStyle().equals("SSU2");
         int cmtu = 0;
         try { 
             String mtu = addr.getOption(PROP_MTU);
             if (mtu != null) {
+                int imtu = Integer.parseInt(mtu);
                 boolean isIPv6 = _host != null && _host.contains(":");
-                cmtu = MTU.rectify(isIPv6, Integer.parseInt(mtu));
+                if (isIPv6 && imtu > 1420) {
+                    // fix for brokered tunnels with too big MTU
+                    if (imtu > 1472 && _host.startsWith("2001:470:"))
+                        imtu = 1472;
+                    else if (_host.startsWith("2a06:a004:"))
+                        imtu = 1420;
+                }
+                if (ssu2only) {
+                    // 1280 min is not enforced here, so that it may be
+                    // rejected in OES2 constructor and IES2.gotRI()
+                    cmtu = Math.min(imtu, PeerState2.MAX_MTU);
+                } else {
+                    cmtu = MTU.rectify(isIPv6, imtu);
+                }
             }
         } catch (NumberFormatException nfe) {}
         _mtu = cmtu;
@@ -126,7 +141,6 @@ class UDPAddress {
         InetAddress[] cintroAddresses = null;
         long[] cintroExps = null;
         Hash[] cintroHashes = null;
-        final boolean ssu2only = addr.getTransportStyle().equals("SSU2");
         final boolean ssu2enable = SSU2Util.ENABLE_RELAY && (ssu2only || "2".equals(addr.getOption("v")));
         for (int i = MAX_INTRODUCERS - 1; i >= 0; i--) {
             // This is the only one required for SSU 1 and 2