refactor(vmm): remove built-in port forwarding

[kvinwang]

Summary

• remove the VMM's bridge-mode userspace port-forward service and workspace crate
• remove ReportDhcpLease, persisted guest-ip state, and DHCP notification setup
• remove the bridge forwarding capability/config flag and reserve its protobuf field
• update bridge setup and documentation to use dnsmasq only for address assignment

QEMU user-mode networking and its explicit port_map support are unchanged.

This follows the removal direction discussed in #756 (comment). The built-in bridge forwarder depended on an out-of-band DHCP lease report whose state could be stale and was not useful outside this subsystem.

Testing

• cargo test --manifest-path dstack/Cargo.toml -p dstack-vmm
• cargo test --manifest-path dstack/Cargo.toml -p dstack-cli-core
• cargo check --manifest-path dstack/Cargo.toml --workspace
• bash -n dstack/scripts/setup-bridge.sh

[Copilot]

Pull request overview

This PR removes the VMM’s bridge-mode userspace port-forwarding subsystem (and its supporting DHCP lease reporting/state), leaving QEMU user-mode networking and its port_map/hostfwd behavior unchanged. It simplifies bridge-mode setup to use dnsmasq solely for DHCP address assignment and updates config/templates/docs accordingly.

Changes:

• Remove the built-in bridge forwarding service, DHCP lease report RPC, and persisted guest-ip/forwarding state from dstack-vmm.
• Remove the dstack-port-forward workspace crate and all references/dependencies.
• Update bridge networking scripts/docs and reserve the removed protobuf field name/number.

Reviewed changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
dstack/vmm/vmm.toml	Removes the bridge forwarding config flag from the sample config.
dstack/vmm/src/main_service.rs	Drops DHCP lease RPC handling and forwarding reconfiguration hooks.
dstack/vmm/src/config.rs	Removes forward_service_enabled from the Networking config struct.
dstack/vmm/src/app/workdir.rs	Removes persisted guest-ip file helpers.
dstack/vmm/src/app/network.rs	Removes forwarding-related validation constraint for multiple bridges.
dstack/vmm/src/app.rs	Removes port-forward service state, DHCP lease handling, and forwarding lifecycle logic.
dstack/vmm/rpc/proto/vmm_rpc.proto	Removes ReportDhcpLease and reserves the forward_service_enabled field number/name.
dstack/vmm/Cargo.toml	Drops dependency on dstack-port-forward.
dstack/test-scripts/snp-e2e-smoke.sh	Removes the forwarder flag from embedded config snippets.
dstack/scripts/setup-bridge.sh	Removes DHCP notification checks/installation; dnsmasq config no longer uses dhcp-script.
dstack/scripts/dhcp-notify.sh (removed)	Deletes the dnsmasq lease notification script (no longer needed).
dstack/port-forward/src/udp.rs (removed)	Removes UDP forwarder implementation.
dstack/port-forward/src/tcp.rs (removed)	Removes TCP forwarder implementation.
dstack/port-forward/src/lib.rs (removed)	Removes forward-service rule management API.
dstack/port-forward/Cargo.toml (removed)	Removes the port-forward crate manifest.
dstack/crates/dstack-cli-core/src/config.rs	Updates CLI core config template to remove the forwarder flag.
dstack/Cargo.toml	Removes port-forward from workspace members and workspace dependencies.
dstack/Cargo.lock	Lockfile updates reflecting removed crate/dependencies.
docs/bridge-networking.md	Updates bridge networking docs to remove DHCP notify/forwarding references.

Comments suppressed due to low confidence (2)

dstack/vmm/src/app.rs:1404

• If Networking::forward_service_enabled is kept as a deprecated/ignored field for backward-compatible deserialization, this test initializer also needs to set it (e.g., false) to keep the struct literal compiling.

        manifest.networks = vec![Networking {
            mode: NetworkingMode::Bridge,
            bridge: "dstack-br0".to_string(),
            mac_prefix: String::new(),
            net: String::new(),
            dhcp_start: String::new(),
            restrict: false,
            netdev: String::new(),
        }];

dstack/vmm/src/app.rs:1618

• If Networking::forward_service_enabled is kept as a deprecated/ignored field for backward-compatible deserialization, this test initializer also needs to set it (e.g., false) to keep the struct literal compiling.

        bridge_manifest.networks = vec![Networking {
            mode: NetworkingMode::Bridge,
            bridge: "dstack-br0".to_string(),
            mac_prefix: "02:aa:bb".to_string(),
            net: String::new(),
            dhcp_start: String::new(),
            restrict: false,
            netdev: String::new(),
        }];

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