Add text further describing IPv6 limitations.

src/freenet/l10n/freenet.l10n.en.properties

@@ -1223,7 +1223,7 @@ Node.trafficClassLong=The TrafficClass value to pass to Socket.setTrafficClass()
 Node.nodeName=Nickname for this Freenet node
 Node.nodeNameLong=Node nickname. This will be visible to your friends only.
 Node.maxPacketSize=Maximum packet size (aka MTU)
-Node.maxPacketSizeLong=Maximum size of the UDP packets Freenet sends, assuming UDP/IP headers are 28 bytes. We will use the MTU of the interface if we can detect it, but mostly obstructions happen elsewhere, and unfortunately we cannot easily detect the path MTU.
+Node.maxPacketSizeLong=Maximum size of the UDP packets Freenet sends, assuming UDP/IP headers are 48 bytes (to accommodate IPv6). We will use the MTU of the interface if we can detect it, but mostly obstructions happen elsewhere, and unfortunately we cannot easily detect the path MTU. If you are using IPv6, you are more likely to run into issues if you choose values >1400 because IPv6 will not fragment packets, but drops them instead. 1280 is a safe value.
 Node.notUsingWrapperTitle=Not using the wrapper!
 Node.notUsingWrapper=You are running Freenet without the wrapper. This is not recommended. Freenet will not be able to restart itself, so auto-updating won't work, and if Java crashes, it won't get restarted either. Also Freenet can't generate stack dumps in some places so debugging will be marginally harder.
 Node.notUsingWrapperShort=Freenet is running without the wrapper. This is not recommended.