There is an 8 byte write only field and some separated flag bits that trigger another 8 bytes of extra alignment padding that are not necessary. There are also a couple of fields that are only used on the server side and others only used on the client side. These fields could be overlaid, with 24 bytes easily saved. This is important on systems where 100's of thousands of these structures get allocated.
My first comment will show one approach for coalescing all the flag bits into a single 64 bit flag word.
Improvement
Minor