set_nspawn_flags said PRIVATE_NETWORK was forced 0 for web-UI
reachability; it is now unconditionally 1 and the UI is reached over the
bridge. write_bridge_dns_marker said it writes or removes the marker;
the removal path went with the host-netns case.
Neither was reachable by the sweeps that found the earlier ones: this
prose describes the *value in words* ('forced 0'), not the code's
literal PRIVATE_NETWORK=0, and neither names the env var. Found by
reading the doc comment of every function whose body this branch
changed.
bb732a106c