Previously, a DAD event would not be sent if DAD was disabled.
This allows integrators to do some work when an IPv6 address is bound to
a NIC without special logic that checks if DAD is enabled.
Without this change, integrators would need to check if a NIC has DAD
enabled when an address is auto-generated. If DAD is enabled, it would
need to delay the work until the DAD completion event; otherwise, it
would need to do the work in the address auto-generated event handler.
Test: stack_test.TestDADDisabled
PiperOrigin-RevId: 293732914
ca30dfa065