Clear p_stops upon PROCFS_CTL_DETACH, similar to r283889.

Noticed by:	jhb
Reviewed by:	sef
Sponsored by:	iXsystems, Inc.
MFC after:	2 weeks

sys/fs/procfs/procfs_ctl.c

@@ -235,6 +235,7 @@ procfs_control(struct thread *td, struct proc *p, int op)
 		} else
 			PROC_LOCK(p);
 		p->p_oppid = 0;
+		p->p_stops = 0;
 		p->p_flag &= ~P_WAITED;	/* XXX ? */
 		sx_xunlock(&proctree_lock);