-- binary
01 00 # version / type
00 08 # length
12 34 56 78 # xid
-- python
ofp.message.hello(xid=0x12345678)
-- c
obj = of_hello_new(OF_VERSION_1_0);
of_hello_xid_set(obj, 305419896);
-- java
builder.setXid(0x12345678)