periodic: Make security diff(1) output as small is possible

Make, by default, security diff(1) produce a unified output with a context of
zero (0) lines. This reduces output of unrelated lines in e-mails delivered
to root.

PR:		270266
Approved by:	jrm (mentor), karels
MFC after:	1 month
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D43071

(cherry picked from commit 3aa71ea7c2)

share/man/man5/periodic.conf.5

@@ -23,7 +23,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd November 7, 2020
+.Dd December 31, 2023
 .Dt PERIODIC.CONF 5
 .Os
 .Sh NAME
@@ -813,7 +813,8 @@ Set to the arguments to pass to the
 .Xr diff 1
 utility when generating differences.
 The default is
-.Fl b u .
+.Fl b
+.Fl U Cm 0 .
 .It Va security_status_chksetuid_enable
 .Pq Vt bool
 Set to

usr.sbin/periodic/periodic.conf

@@ -251,7 +251,7 @@ security_show_badconfig="NO"				# scripts returning 2
 # These options are used by the security periodic(8) scripts spawned in
 # daily and weekly 450.status-security.
 security_status_logdir="/var/log"			# Directory for logs
-security_status_diff_flags="-b -u"			# flags for diff output
+security_status_diff_flags="-b -U 0"			# flags for diff output
 
 # Each of the security_status_*_period options below can have one of the
 # following values: