Just because we don't have known endpoints for a peer does not mean that
the peer should become unreachable. If we know the peers key, it should
be able to call us, then we can talk back via whatever path it called us
on. First step - don't drop the packet in this context.
Updates tailscale/corp#19106
Signed-off-by: James Tucker <james@tailscale.com>
a2eb1c22b0