Don't set network/security mode on stable dockerfile

Signed-off-by: Andy Caldwell <andrew.caldwell@metaswitch.com>

frontend/dockerfile/dockerfile2llb/convert.go

@@ -644,7 +644,9 @@ func dispatchRun(d *dispatchState, c *instructions.RunCommand, proxy *llb.ProxyE
 	if err != nil {
 		return err
 	}
-	opt = append(opt, securityOpt)
+	if securityOpt != nil {
+		opt = append(opt, securityOpt)
+	}
 
 	networkOpt, err := dispatchRunNetwork(c)
 	if err != nil {

frontend/dockerfile/dockerfile2llb/convert_norunnetwork.go

@@ -5,9 +5,8 @@ package dockerfile2llb
 import (
 	"github.com/moby/buildkit/client/llb"
 	"github.com/moby/buildkit/frontend/dockerfile/instructions"
-	"github.com/moby/buildkit/solver/pb"
 )
 
 func dispatchRunNetwork(c *instructions.RunCommand) (llb.RunOption, error) {
-	return llb.Network(pb.NetMode_UNSET), nil
+	return nil, nil
 }

frontend/dockerfile/dockerfile2llb/convert_norunsecurity.go

@@ -5,9 +5,8 @@ package dockerfile2llb
 import (
 	"github.com/moby/buildkit/client/llb"
 	"github.com/moby/buildkit/frontend/dockerfile/instructions"
-	"github.com/moby/buildkit/solver/pb"
 )
 
 func dispatchRunSecurity(c *instructions.RunCommand) (llb.RunOption, error) {
-	return llb.Security(pb.SecurityMode_SANDBOX), nil
+	return nil, nil
 }