According to style(9):
> normally, include <sys/types.h> OR <sys/param.h>, but not both.
(<sys/param.h> already includes <sys/types.h> when LOCORE is not defined).
We have an nitems() macro in the <sys/param.h> header that is
convenient to re-use as it makes things easier to read.
Given that it is available already without adding additional
headers and other parts of libc already use it, extend a bit
more its use.
