barebox: update kernel cmdline in boot-nand script

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>

patches/barebox/env/bin/boot-nand

@@ -4,6 +4,7 @@
 cp /dev/nand0.kernel.bb /dev/mem.kernel
 bootargs="console=ttyS0,115200 panic=10 mem=64M"
 bootargs="$bootargs root=/dev/mtdblock1 rootfstype=jffs2"
+bootargs="$bootargs wr_nic.macaddr=$macaddr"
 bootz /dev/mem.kernel
 
 # If it don't boot, show the menu