[source] bcm53xx: add missing system.sh include

[LEDE Commits]

rmilecki pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/083854f06f0c340bd63ad5c75a8afa7fc97d9b38

commit 083854f06f0c340bd63ad5c75a8afa7fc97d9b38
Author: Rafał Miłecki <rafal at milecki.pl>
AuthorDate: Tue Feb 7 11:43:49 2017 +0100

    bcm53xx: add missing system.sh include
    
    It's needed for macaddr_add.
    
    Fixes: 5ed23223fd1f ("bcm53xx: set WAN MAC address to don't share one with LAN interface")
    Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
 target/linux/bcm53xx/base-files/etc/board.d/02_network | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/linux/bcm53xx/base-files/etc/board.d/02_network b/target/linux/bcm53xx/base-files/etc/board.d/02_network
index fa2837c..89bd544 100755
--- a/target/linux/bcm53xx/base-files/etc/board.d/02_network
+++ b/target/linux/bcm53xx/base-files/etc/board.d/02_network
@@ -3,6 +3,7 @@
 # Copyright (C) 2011 OpenWrt.org
 #
 
+. /lib/functions/system.sh
 . /lib/functions/uci-defaults.sh
 
 board_config_update