net/litep2p: Propagate ValuePut events to the network backend (#5018)

The `DhtEvent::ValuePut` was not propagated back to the higher levels.

This PR ensures we'll send the ValuePut event similarly to
`DhtEvent::ValuePutFailed`

### Next Steps
- [ ] A bit more testing

Thanks @alexggh for catching this 

 

cc @paritytech/networking

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>