tools/xenstored: fix live update with watches specifying depth

Due to a typo the state record for a watch specifying a depth is
written only partially. Instead of using the correct length of the
xs_state_watch_ext structure only the length of the xs_state_watch
structure was used when writing the data.

Fix that by using the correct length.

This is XSA-514 / CVE-2026-79607

Fixes: db98de120c ("tools/xenstored: add depth information to watches")
Reported-by: Andrii Sultanov <andriy.sultanov@vates.tech>
Signed-off-by: Juergen Gross <jgross@suse.com>

tools/xenstored/watch.c

@@ -354,7 +354,7 @@ const char *dump_state_watches(FILE *fp, struct connection *conn,
 			return "Dump watch state error";
 
 		if (watch->depth >= 0) {
-			if (fwrite(&swe, sizeof(sw), 1, fp) != 1)
+			if (fwrite(&swe, sizeof(swe), 1, fp) != 1)
 				return "Dump watch state ext error";
 		} else {
 			if (fwrite(&sw, sizeof(sw), 1, fp) != 1)