PiotrB I'm was able to got my hands on the edison last week, I'm still on setting things up.
But your question isn't edison specific. The bluetooth Header file ist part of the Bluez-dev package, so you need this package. After a quick look on Index of /edison/repo/core2-32 there is a bluez5-dev package (and several other bluez related packages). So if you have followed Edison Package Repo Configuration Instructions than a "opkg install bluez5-dev" should do the trick to get the header file.