• Replace N(a)/N(i)/N(T)/LEN(a)/ARRAY_SIZE(a) with nitems()
• Add missing <err.h> for err() and <sys/sysctl.h> for sysctlbyname()
• NULL -> 0 for 5th parameter of sysctlbyname()

Submitted by: Andriy Voskoboinyk <s3erios@gmail com>
Differential Revision: https://reviews.freebsd.org/D3442