Fix armbian-firstrun service not disabled on start.

Fixes: 7b33243c27

Signed-off-by: Viacheslav Bocharov <adeep@lexina.in>

packages/bsp/common/usr/lib/armbian/armbian-common

@@ -40,7 +40,7 @@ set_fixed_mac ()
 
 	# we use random mac routine only with sytemd-network.
 	if ! grep 'renderer: networkd' /etc/netplan/*.yaml >/dev/null; then
-		exit 0
+		return
 	fi
 
 	local netplan_config_file="/etc/netplan/20-eth-fixed-mac.yaml"