unetmsg: fix publish notification timing around remote auth

unetmsg: fix publish notification timing around remote auth

When a remote peer's publish registrations arrive via RX before the
local TX connection is authenticated, handle_publish fires but the
subscriber can't reach the remote publisher yet since the TX channel
isn't ready.

Suppress publish notifications on the RX side when no authenticated TX
channel exists for the remote host. After TX authentication completes,
re-trigger handle_publish only for topics that the specific peer
publishes and that have local subscribers.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry picked from commit 3efcf444a11e9402d86ae79c733114827ce31b42)