dhcp: set TERMINATED state when the client is stopped
NM_DHCP_STATE_DONE is for when the client reports that it is shutting down. If we manually stop it, we should set the TERMINATED state, so that NMDevice doesn't start a grace period waiting for a renewal.
This fixes the:
device (enp1s0): DHCPv4: trying to acquire a new lease within 90 seconds
message printed when NM is shutting down.