netinfo: Only report bootproto4=dhcp when we have an address

A DHCPv4 lease might still be valid. As the address is unused, however,
it cannot be said that the interface has been configured using DHCPv4.

Change-Id: I3da566a4ecbc17b704103a715697a63fee0cdd15
Signed-off-by: Ondřej Svoboda <osvoboda@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31568
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>