pb: Rewrite object reading to use pb-descs

The pb_read thing is no longer a macros. This will allow to
factor out objects collecting on restore.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

uts_ns.c

@@ -48,7 +48,7 @@ int prepare_utsns(int pid)
 	if (fd < 0)
 		return -1;
 
-	ret = pb_read(fd, &ue, utsns_entry);
+	ret = pb_read_one(fd, &ue, PB_UTSNS);
 	if (ret < 0)
 		goto out;