[bbagent] monitor invokeCh in a go routine
[bbagent] monitor invokeCh in a go routine

Bug: 1222736
Change-Id: Iea13b1dcb6e0752bdd837afc55cac01a242e8b1a
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3585358
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Chan Li <332b6c56634d0f63001046c664a2370006a02420@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go