ifup: fix <child> subnode of <match> generation

It should not check the w->device existance.
ifup: generate <link-type> directly from <device> gen.
dhcp4: use address class netmask if missed (bnc#887586)
Merge pull request #327 from pwieczorkiewicz/match_fix
Merge pull request #328 from mtomaschewski/dhcp4-no-netmask