Make connection lookup calls consistent in 04-channel

[damiannolan]

Summary

The 04-channel submodule has inconsistent usage of k.GetConnection() and k.connectionKeeper.GetConnection() in order to lookup a connectionEnd.

See thread

Make usage consistent across handshake and upgrade handlers.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[DimitrisJim]

Related but non-blocking: #3466

[crodriguezvega]

I think my preference here would be the following:

If I am not mistaken, the GetConnection function was added so that channel keeper implementation satisfies the ChannelKeeper interface declared in ics27 and we can retrieve the connection via the channel keeper in ics27. Then maybe we could by-convention restrict its usage to that use? Another thing is that if we use GetConnection in 04-channel then the error of not finding the connection is wrapped one more time (maybe unnecessarily)? If connectionKeeper.GetConnection doesn't find the connection, then an error is returned and in channel keeper's GetConnection that error is wrapped.

[DimitrisJim]

Yeah, I see we wrap in the most recent usages of GetConnection (i.e in upgrade.go). I guess it isn't all that necessary really (and kinda beats the point of having GetConnection handle the error uniformly for us).

Personally, I don't mind using channelKeeper.GetConnection since it's there already.

[crodriguezvega]

We will use k.connectionKeeper.GetConnection.

[crodriguezvega]

Closed by #4146.