Move sysctl.conf to sbin/sysctl/ and switch to CONFS.

This helps with pkgbase to tag this config file as a config file.

Approved by:	allanjude (mentor), will (mentor)
Differential Revision:	https://reviews.freebsd.org/D16559

etc/Makefile

@@ -41,7 +41,6 @@ BIN1=	crontab \
 	remote \
 	rpc \
 	services \
-	sysctl.conf \
 	syslog.conf \
 	termcap.small
 

sbin/sysctl/Makefile

@@ -2,6 +2,7 @@
 # $FreeBSD$
 
 PACKAGE=runtime
+CONFS=	sysctl.conf
 PROG=	sysctl
 WARNS?=	3
 MAN=	sysctl.8