fix: use getChannel instead of getConnection for channel queries

[Lil-Duckling-22]

Motivation

The channel handshake logic in pendingDatagrams incorrectly uses getConnection() with a non-existent counterpartyIdentifier field when querying channels. This breaks the example code since ChannelEnd doesn't have counterpartyIdentifier—it uses counterpartyPortIdentifier and counterpartyChannelIdentifier.

Solution

Replace counterparty.getConnection(localEnd.counterpartyIdentifier) with counterparty.getChannel(localEnd.counterpartyPortIdentifier, localEnd.counterpartyChannelIdentifier) to correctly query the counterparty channel end using the proper method and fields from the ChannelEnd structure.