Fix preseed MAC address fetch method

Fix preseed MAC address fetch method

JIRA: -

e.g.:

root@host1:~# ip link show eth4
6: eth4: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ec:38:8f:79:fa:5c brd ff:ff:ff:ff:ff:ff
root@host1:~# echo $(echo $@ | cut -d' ' -f17)
ec:38:8f:79:fa:5c

root@host4:~# ip link show eth4
6: eth4: <BROADCAST,MULTICAST> mtu 1500 qdisc noop portid 0100000000000000000000000000003000 state DOWN mode DEFAULT group default qlen 1000
    link/ether e0:36:76:d2:34:73 brd ff:ff:ff:ff:ff:ff
root@host4:~# echo $(echo $@ | cut -d' ' -f17)
1000
root@host4:~# echo $(echo $@ | cut -d' ' -f19)
e0:36:76:d2:34:73

Change-Id: I916c19807da724e9ba471376f81f3c763b9340d5
Signed-off-by: QiLiang <liangqi1@huawei.com>