Backport PR
#6003: Set kernel_id before checking websocket...
Backport PR
#6003: Set kernel_id before checking websocket
If websocket attempt fails and cross origin attempt is detected, a HTTPError(404) error is raised. However, in the process of closing connections because of this 404 error, an unhandled Attribute exception (kernel_id not an attribute) is raised. Setting the kernel_id first avoids this.
