Only issue a single dhcp requests per interface with the host-name

Only issue a single dhcp requests per interface with the host-name
option set. Remove the second request, which does not provide the
host-name option. The client supplied hostname is used in certain
setups by DHCP servers to update DNS records on behalf of clients
and ensures that the hostname information is in the lease db.

discussed with deraadt
ok krw@ halex@