Interfaces with no ip are not allowed to run dhcp server. bnc#887139

According RFC 2131 each DHCP server has to send its own ip address in
the 'server identifier' option. So it makes no sense to set dhcp server
on top of BOOTPROTO=none and/or BOOTPROTO=static (with empty IPADDR).
Minor cleanup
Added comment
Updated changelog
More cleanup in CardSelectionValidate
Merge pull request #4 from mchf/bnc887139-unconfigured-interfaces

Allow ip aware interfaces for selection only