images: save process pid which opens pidfd

We use this pid while restoring pidfds that point to dead processes.

Signed-off-by: Bhavik Sachdev <[email protected]>

images/pidfd.proto

@@ -10,4 +10,5 @@ message pidfd_entry {
 	required uint32		flags		= 3;
 	required int32		nspid		= 4;
 	required fown_entry	fown		= 5;
+	required uint32		pidfd_owner	= 6;
 }