fix incorrect option code when serializing Capwap_ac_v4 option

[yomimono]

No description provided.

[haesbaert]

Merged, I've commited a line by line copyrights since I prefer that format, also added you to dhcp_wire.ml and test.ml, please let me know if this is ok.

I don't really know what's the norm on the ocaml community concerning copyrights.
I'm used to add myself to a file when I've done "enough" (I think this is a UNIX tradition thingy), and keep track of copyrights on a file by file basis. So if anyone wants to relicense some day, they need to contact every author of every file.

[yomimono]

I also don't really know what the norm is concerning copyrights; I've pretty much been putting my name in stuff that I write, and if someone else adds me to something that I worked on a lot, that's fine. I have banner blindness for top-of-file copyrights and I have to admit I didn't even notice that there were any in this repo!