objectmodel: removed unused hwaddr interface property
hwaddr: set link-address on ethernet,vlan,macvlan
mtu: skip if up, limit it to mtu of lower device

- Use separate calls to set the mtu and the link up
- Do not allow to set higher mtu than on lower device.
- Do not set, when interface is already UP (->reload);
  it causes busy errors and breaks upper interfaces.
compat: process ethtool options ifcfg variable
compat: check ethernet pointer before generating
Merge pull request #147 from mtomaschewski/hwaddr-change