[client] fix unused-helper lint after the privileged test split

Splitting privileged tests into *_privileged_test.go left their shared helpers in
the untagged files, so in the default (no-tag) build they had no callers and
golangci-lint flagged them as unused.

Moved the privileged-only helpers into the privileged files next to their callers
(generateDummyHandler; createEngine/startSignal/startManagement/getConnectedPeers/
getPeers + kaep/kasp; (*mockDaemon).setJWTToken). Annotated the shared routing-test
fixtures that must stay untagged for cross-platform compilation with //nolint:unused
(systemops_bsd expected* vars, ensureIPv6DefaultRoute on bsd/windows,
loopbackIfaceWindows), matching the existing linux variant.

client/ssh/proxy/proxy_privileged_test.go

@@ -33,6 +33,10 @@ import (
 	sshuserhash "github.com/netbirdio/netbird/shared/sshauth"
 )
 
+func (m *mockDaemon) setJWTToken(token string) {
+	m.impl.jwtToken = token
+}
+
 func TestSSHProxy_Connect(t *testing.T) {
 	if testing.Short() {
 		t.Skip("Skipping integration test in short mode")

client/ssh/proxy/proxy_test.go

@@ -150,10 +150,6 @@ func (m *mockDaemon) setHostKey(addr string, pubKey []byte) {
 	m.impl.hostKeys[addr] = pubKey
 }
 
-func (m *mockDaemon) setJWTToken(token string) {
-	m.impl.jwtToken = token
-}
-
 func (m *mockDaemon) stop() {
 	if m.server != nil {
 		m.server.Stop()