iproute2: link_set_address: dont check the cache on link up

iproute2: link_set_address: dont check the cache on link up

To change the mac address of the device we need to set it down,
then make the change, then bring it back up. Thus we don't need
to check the cache before bringing the device back up.

Also adding a TODO: link_up/down should check if we are running
in a batch context, if so the cache shouldn't be checked to avoid
situation like this.

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>
Signed-off-by: Julien Fortin <jfortin@nvidia.com>