Fix bonding and actually enable ETHTOOL_OPTS

Fix bonding and actually enable ETHTOOL_OPTS

1. Applying ETHTOOL_OPTS was inside a code block only run for bond
slaves. This is now fixed.
2. Dependency on 'ifenslave' for bonding device configuration was
dropped. Use iproute2 instead.
3. ifup/ifdown behavior for bondX and enslaved devices was fixed. Both
commands should be symmetrical: running 'ifdown SOMEIF; ifup SOMEIF'
should get SOMEIF as close to what its state was before ifdown as is
possible. This was very not the case.