[invirt-dhcp] Improve standards compliance Provide a server-identifier option containing our IP address, as is required by several DHCP clients including gPXE (used for the Debathena network install CD) and Windows. Reuse the existing DHCP socket in a bindtodevice - sendto - restore global binding sequence, instead of creating a new socket for each reply, in order to keep replies coming from port 67. This is required by the standard, some client programs, and all DHCP forwarders. svn path=/trunk/packages/invirt-dhcp/; revision=2491