DHCP snooping table update for changed MAC address

The DHCP snooping table is updated in the event of a change to a client's MAC address. If a client requests for an IP address that matches an IP address in the DHCP snooping table, but has a MAC address that does not match the one bound to that IP address in the DHCP snooping table, then a placeholder binding is created using the client IP address and the new MAC address. When the switch receives a DHCPACK message from the DHCP server, this binding is added to the DHCP snooping table, replacing the original binding. This new feature requires no configuration changes to be made by the user.