add the MKNET variable to select a network stack

The MKNET variable can be used to select the network stack you want to
build and install with OpenRC.

The current default is the gentoo "oldnet" stack. If you want to install
the OpenRC newnet stack, use MKNET=newnet on the make command line.

runlevels/Makefile

@@ -1,5 +1,5 @@
-BOOT=		bootmisc fsck hostname localmount network \
-		root staticroute swap swapfiles sysctl urandom ${BOOT-${OS}}
+BOOT=		bootmisc fsck hostname localmount \
+		root swap swapfiles sysctl urandom ${BOOT-${OS}}
 DEFAULT=	local netmount
 SHUTDOWN=	savecache ${SHUTDOWN-${OS}}
 SYSINIT=	${SYSINIT-${OS}}
@@ -10,6 +10,16 @@ BOOTDIR=	${LEVELDIR}/boot
 DEFAULTDIR=	${LEVELDIR}/default
 SHUTDOWNDIR=	${LEVELDIR}/shutdown
 
+ifeq (${MKNET},)
+BOOT-FreeBSD += net.lo0
+BOOT-Linux += net.lo
+BOOT-NetBSD += net.lo0
+endif
+
+ifeq (${MKNET},newnet)
+BOOT+= network staticroute
+endif
+
 INITDIR=	../init.d
 
 MK=		../mk