[Bug]: Error restarting gateway connections

[jvstme]

Steps to reproduce

1. Create a gateway.
2. Switch off the network on dstack-server's host and wait a few minutes (~5) until you see these messages in server logs:

Connection to gateway 0.0.0.0 failed: ssh: connect to host 0.0.0.0 port 22: Network is unreachable

1. Switch the network back on.

Actual behaviour

The connection is never restarted, new errors appear in server logs when trying to restart. That means new services cannot be registered, old services don't work unless they are auth: false.

Expected behaviour

The connection is restarted soon after network is restored.

dstack version

master

Server logs

[00:24:23] INFO     dstack._internal.server.services.gateways.connection:81 Connection to gateway 0.0.0.0 is down, restarting                                                
[00:24:24] DEBUG    dstack._internal.core.services.ssh.tunnel:218 SSH tunnel failed: b"Warning: Permanently added '0.0.0.0' (ED25519) to the list of known hosts.\r\nError: remote port forwarding failed for listen path /home/ubuntu/dstack/server-connections/1f76da7e-77ef-4f36-97c1-585e87d2a42b.sock\r\n"                                                                               
           ERROR    dstack._internal.server.background.tasks.process_gateways:89 Connection to gateway 0.0.0.0 failed: Error: remote port forwarding failed for listen path /home/ubuntu/dstack/server-connections/1f76da7e-77ef-4f36-97c1-585e87d2a42b.sock

Additional information

Reason: the unix socket used for reverse forwarding remains on the gateway and prevents opening new connections with the same socket path.
Workaround: restart dstack server, it will generate a new socket path.