device: avoid taking down link to change MAC address

A lot of drivers actually support changing the MAC address of a link
without taking it down.

Taking down a link is very bad, because kernel will remove routes
and IPv6 addresses.

For example, if the user used a dispatcher script to add routes,
these will be lost. Note that we may change the MAC address of a
device any time. For example, a VLAN device watches the parent's
MAC address and configures it (with a logging message "parent hardware
address changed to ...").

Try first whether we can change the MAC address without taking the
link down. Only if that fails, retry with taking it down first.
5 jobs for th/device-set-mac-addr-no-down in 29 minutes and 36 seconds (queued for 30 minutes and 23 seconds)