Support discv5 call which don't need response

[GrapeBaBa]

Right now portal network use discv5 based utp packet and it only use talkReq but no need response. Currently in geth code, callCh is used for discv5 request with response, sendCh is used for discv5 response.

Reuse sendCh to send calls that don't require a response, this is a minimal change.

[devlongs]

Hi @GrapeBaBa can I work on this issue?

[GrapeBaBa]

@devlongs Thanks, however this is what we already added in shisui and need to migrate into the geth code base.