Build a "cdrom" installer and not a "netboot" one

In the live-build code, netinst and netboot have the same meaning,
and it means netboot, an installer that fetches the d-i udebs over
the network. But we don't want that, we want the udeb to be available
in the ISO so that it keeps working even after a kernel update in
kali-rolling.

auto/config

@@ -72,10 +72,10 @@ fi
 # Define options that vary across architectures
 case "$arch" in
     amd64)
-	lb_opts="$lb_opts --debian-installer netinst"
+	lb_opts="$lb_opts --debian-installer cdrom"
     ;;
     i386)
-	lb_opts="$lb_opts --debian-installer netinst --linux-flavours 686-pae"
+	lb_opts="$lb_opts --debian-installer cdrom --linux-flavours 686-pae"
     ;;
     armel|armhf)
 	lb_opts="$lb_opts --binary-images hdd --binary-filesystem ext4 --chroot-filesystem none"