Address allocation method determines behavior when address pool is deleted or drained

Additional checking is performed to determine the subsequent behavior when authd notifies the DHCP process that an address pool is deleted or being drained. When addresses are allocated on demand, the family with the address in that pool is logged out immediately when the pool is deleted, or logged out gracefully by the draining process when a DHCP renew or rebind message is received. When the addresses are preallocated, the addresses for both families are deleted immediately when the pool is deleted, or deleted gracefully by the draining process when a DHCP renew or rebind message is received.