sandbox: net: Add mac address for eth8 to environment

The phy_eth0 interface introduced in commit f3dd213e15 ("net: introduce
helpers to get PHY ofnode from MAC") uses a globally-administered
address. Switch to using a locally-administered address, and add it to
the sandbox environment, like the others.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
diff --git a/board/sandbox/sandbox.env b/board/sandbox/sandbox.env
index b4c0463..6dedc75 100644
--- a/board/sandbox/sandbox.env
+++ b/board/sandbox/sandbox.env
@@ -11,6 +11,7 @@
 eth4addr=02:00:11:22:33:48
 eth5addr=02:00:11:22:33:46
 eth6addr=02:00:11:22:33:47
+eth8addr=02:00:11:22:33:49
 ipaddr=192.0.2.1
 
 /*