signals: cosmetic, collect_signal: use SI_USER

Trivial, s/0/SI_USER/ in collect_signal() for grep.

This is a bit confusing, we don't know the source of this signal.
But we don't care, and "info->si_code = 0" is imho worse.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -423,7 +423,7 @@ still_pending:
 		 */
 		info->si_signo = sig;
 		info->si_errno = 0;
-		info->si_code = 0;
+		info->si_code = SI_USER;
 		info->si_pid = 0;
 		info->si_uid = 0;
 	}