thread_single_end(): consistently maintain p_boundary_count for ALLPROC mode

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 week
Differential revision:	https://reviews.freebsd.org/D35310

sys/kern/kern_thread.c

@@ -1673,7 +1673,7 @@ thread_single_end(struct proc *p, int mode)
 			thread_lock(td);
 			if (TD_IS_SUSPENDED(td)) {
 				wakeup_swapper |= thread_unsuspend_one(td, p,
-				    mode == SINGLE_BOUNDARY);
+				    true);
 			} else
 				thread_unlock(td);
 		}