Automatic merge from submit-queue
Move defaulting logic for ExternalTrafficPolicy into defaults.go
Link #45812.
Per [#45812/comment](https://github.com/kubernetes/kubernetes/issues/45812#issuecomment-301632807), move defaulting logic to defaults.go so that federation will get the same code.
This PR does not have any functional change :)
/assign @freehan @thockin
/cc @madhusudancs @nikhiljindal @shashidharatd
Also /cc @caesarxuchao per the client-go changes.
**Release note**:
```release-note
NONE
```