ignore-client-uids dhcpd configuration option added

This help in case multiple DHCP clients, using different client-uid
values are used on a single machine, sometimes during a single boot
process (BIOS PXE client, PXE bootloader, initramfs and final system –
four different DHCP clients). Using the 'ignore-client-uids on' option
will prevent for allocating several different IP addresses in this case,
by slightly breaking the DHCP protocol.

Release: 2