ifconfig/dmesg: Fix MAC address format

For example, if we set MAC address 0e:0f:2b:ec:e8:15,OSv will display
e:f:2b:ec:e8:15 using ifconfig or dmesg command.

Signed-off-by: Haifeng Gao <gaohaifeng.gao@huawei.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>