fix: use correct length 8 for ModifySocialListMessageEncoder

Author: Jameskmonger

src/main/java/org/runejs/client/net/codec/runejs435/encoder/chat/ModifySocialListMessageEncoder.java

@@ -15,7 +15,7 @@ public PacketBuffer encode(ModifySocialListOutboundMessage message) {
         // the structure is the same. This may not be the same for all revisions
         int opcode = this.getOpcode(message);
 
-        PacketBuffer buffer = OutgoingPackets.openFixedSizePacket(4, opcode);
+        PacketBuffer buffer = OutgoingPackets.openFixedSizePacket(8, opcode);
 
         buffer.putLongBE(message.target);