[client] Make Test_ConnectPeers deterministic under Docker/eBPF kernel / Darwin CI (#6884)

## Describe your changes

Make `Test_ConnectPeers` deterministic. Two issues, both surfaced once
the
privileged suite moved into a `--privileged` Docker container (#6425):

1. The peers used `getLocalIP()` as their WireGuard endpoint, i.e. the
host's
routable NIC IP (the docker bridge IP `172.17.0.2` in CI). That address
might
not hairpin reliably inside the container, so the handshake
intermittently
timed out (flaky). Use loopback (`127.1.0.x`) instead — always
self-reachable.
2. On a Linux runner with the WG kernel module the iface uses the eBPF
proxy
factory. Its manager is a singleton with one shared XDP program +
settings
map, so bringing up the two ifaces makes the second factory overwrite
the
first's `wg_port`/`proxy_port` and the handshake is dropped. The test is
   incompatible with the eBPF factory, so disable it via
`NB_DISABLE_EBPF_WG_PROXY` (peers then handshake directly over
loopback).
Running the suite across all three modes (eBPF / UDP proxy / ICE bind)
would
   need a larger refactor.

Also fixes a typo in the `ErrSharedSockStopped` message (`socked` →
`socket`).

## Issue ticket number and link

No public issue — CI flakiness follow-up to #6871 on `Test_ConnectPeers`

(https://github.com/netbirdio/netbird/blob/main/client/iface/iface_test.go).

## Stack

<!-- branch-stack -->

### Checklist
- [x] Is it a bug fix
- [ ] Is a typo/documentation fix
- [ ] Is a feature enhancement
- [ ] It is a refactor
- [ ] Created tests that fail without the change (if possible)

> By submitting this pull request, you confirm that you have read and
agree to the terms of the [Contributor License
Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md).

## Documentation
Select exactly one:

- [ ] I added/updated documentation for this change
- [x] Documentation is **not needed** for this change (explain why)

Test-only change (plus a log-string typo). No public API, CLI, config,
or
behavior change.

### Docs PR URL (required if "docs added" is checked)
Paste the PR link from https://github.com/netbirdio/docs here:

N/A

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Corrected the “shared socket stopped” error message for clearer
output.
* **Tests**
* Improved peer connection test reliability in privileged CI by
disabling the eBPF WireGuard proxy and using fixed loopback UDP
endpoints for deterministic setup.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

client/iface/iface_test.go

@@ -464,6 +464,8 @@ func Test_RemovePeer(t *testing.T) {
 }
 
 func Test_ConnectPeers(t *testing.T) {
+	t.Setenv("NB_DISABLE_EBPF_WG_PROXY", "true")
+
 	peer1ifaceName := fmt.Sprintf("utun%d", WgIntNumber+400)
 	peer1wgIP := netip.MustParsePrefix("10.99.99.17/30")
 	peer1Key, _ := wgtypes.GeneratePrivateKey()
@@ -505,12 +507,8 @@ func Test_ConnectPeers(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	localIP, err := getLocalIP()
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	peer1endpoint, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", localIP, peer1wgPort))
+	localIP1 := "127.0.0.1"
+	peer1endpoint, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", localIP1, peer1wgPort))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -546,7 +544,8 @@ func Test_ConnectPeers(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	peer2endpoint, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", localIP, peer2wgPort))
+	localIP2 := "127.0.0.1"
+	peer2endpoint, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", localIP2, peer2wgPort))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -621,28 +620,3 @@ func getPeer(ifaceName, peerPubKey string) (wgtypes.Peer, error) {
 	}
 	return wgtypes.Peer{}, fmt.Errorf("peer not found")
 }
-
-func getLocalIP() (string, error) {
-	// Get all interfaces
-	addrs, err := net.InterfaceAddrs()
-	if err != nil {
-		return "", err
-	}
-
-	for _, addr := range addrs {
-		ipNet, ok := addr.(*net.IPNet)
-		if !ok {
-			continue
-		}
-		if ipNet.IP.IsLoopback() {
-			continue
-		}
-
-		if ipNet.IP.To4() == nil {
-			continue
-		}
-		return ipNet.IP.String(), nil
-	}
-
-	return "", fmt.Errorf("no local IP found")
-}

sharedsock/sock_linux.go

@@ -24,7 +24,7 @@ import (
 )
 
 // ErrSharedSockStopped indicates that shared socket has been stopped
-var ErrSharedSockStopped = fmt.Errorf("shared socked stopped")
+var ErrSharedSockStopped = fmt.Errorf("shared socket stopped")
 
 // SharedSocket is a net.PacketConn that initiates two raw sockets (ipv4 and ipv6) and listens to UDP packets filtered
 // by BPF instructions (e.g., IncomingSTUNFilter that checks and sends only STUN packets to the listeners (ReadFrom)).