kvm tools: Fill all DHCP options

The following DHCP options are filled.

   - MSG_TYPE

   - SERVER_ID

   - LEASE_TIME

   - SUBMASK

   - ROUTER

   - DNS_SERVER

   - DOMAIN_NAME

Signed-off-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>