monitor: Add latency information per channel

monitor: Add latency information per channel

This attempts to print latency information per channel in addition to
per connection/handle:

> HCI Event: Number of Completed Packets (0x13) plen 5
        Num handles: 1
        Handle: 256 Address: XX:XX:XX:XX:XX:XX
        Count: 1
        Latency: 15 msec (3-39 msec ~18 msec)
        Channel: 68 [PSM 25 mode Basic (0x00)] {chan 2}
        Channel Latency: 15 msec (6-35 msec ~18 msec)