Don't include server_settings.h in fc_interface.h
The fc_interface module needs the sset_type enum and the server_setting_id type to provide its server setting access abstractions. But fc_interface is supposed to be used where the client and the server does things differently yet still needs a common interface. It is already used in many non server setting related places.
Stop pulling in server_settings.h everywhere fc_interface.h is included. Move the sset_type enum and the server_setting_id type to fc_types.h and include them to fc_interface.h from there.