Docker's _connect_nio and adapter_update_nio_binding applied packet
filters but never called _ubridge_apply_markers, so markers silently
did nothing on Docker links despite docker being in the allowlist.
Add the missing calls (same pattern as the IOU fix).
Also narrow _MARKER_CAPABLE_TYPES to the four types that actually
implement marker support — vpcs, qemu, docker, iou — removing
dynamips, virtualbox, vmware, and cloud which have no marker pathway
and would silently fail when selected as the capture side.