• Define true and false in sys/types.h for _KERNEL consumers, and typedef bool. Due to macro expansion it seemed better to use a typedef for kernel consumers (specifically ofed won't compile without more changes if a define is used).
• <stdbool.h> should also not re-define bool/true/false if they are defined by <sys/types.h>. It would probably be a programming error to define _KERNEL for user-space code, but downstream consumers like Isilon have already been including <stdbool.h> in kernel sources, and this protects that usage.
• sizeof(_Bool) is not necessarily the same as sizeof(int), so kernel modules should be rebuild with this change. Bump __FreeBSD_version.

MFC after: 2 weeks
Sponsored by: Isilon Systems, LLC