- avoid unncessary name change requests
The kernel does not check if the specified IFNAME is different
from the current name. It assumes that if IFNAME and ifindex
are both specified, a name change is requested. Therefore avoid
specyfing IFNAME if ifindex is provided and original and new
name are identical.
- move link building to own function (to allow link add later on)
- error if immutable changes have been made
- better documentation