Require p_cansched() for changing a process' protection status via
procctl() rather than p_cansee().

Submitted by:	rwatson
MFC after:	3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272449 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f