Remove BSD and USL copyright and update license block in in_prot.c, as the
code in this file was written by Robert N. M. Waston.

Move cr_can* prototypes from sys/systm.h to sys/proc.h

Reported by: rwatson
Reviewed by: rwatson
Approved by: sjg (mentor)
Differential Revision: https://reviews.freebsd.org/D7345