[client] Add --disable-networks flag to block network selection (#5896)

client/server/network.go

@@ -9,6 +9,8 @@ import (
 	"strings"
 
 	"golang.org/x/exp/maps"
+	"google.golang.org/grpc/codes"
+	gstatus "google.golang.org/grpc/status"
 
 	"github.com/netbirdio/netbird/client/proto"
 	"github.com/netbirdio/netbird/route"
@@ -27,6 +29,10 @@ func (s *Server) ListNetworks(context.Context, *proto.ListNetworksRequest) (*pro
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
+	if s.networksDisabled {
+		return nil, gstatus.Errorf(codes.Unavailable, errNetworksDisabled)
+	}
+
 	if s.connectClient == nil {
 		return nil, fmt.Errorf("not connected")
 	}
@@ -118,6 +124,10 @@ func (s *Server) SelectNetworks(_ context.Context, req *proto.SelectNetworksRequ
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
+	if s.networksDisabled {
+		return nil, gstatus.Errorf(codes.Unavailable, errNetworksDisabled)
+	}
+
 	if s.connectClient == nil {
 		return nil, fmt.Errorf("not connected")
 	}
@@ -164,6 +174,10 @@ func (s *Server) DeselectNetworks(_ context.Context, req *proto.SelectNetworksRe
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
+	if s.networksDisabled {
+		return nil, gstatus.Errorf(codes.Unavailable, errNetworksDisabled)
+	}
+
 	if s.connectClient == nil {
 		return nil, fmt.Errorf("not connected")
 	}