The `name' and `newp' arguments can be marked const, because the buffers
they refer to are never changed. While there, perform some other
cleanups:
- Remove K&R from sysctl.c.
- Implement sysctlbyname() using sysctlnametomib() to prevent
duplication of an undocumented kernel interface.
- Fix some whitespace nits.
It seems the prototypes are now in sync with NetBSD as well.