soqinsque(): replace 'DIAGNOSTIC' block by KASSERT(9)

[Vitaliy Makkoveev]

Just for consistency with the rest of kern/uipc_socket2.c

Index: sys/kern/uipc_socket2.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_socket2.c,v
retrieving revision 1.113
diff -u -p -r1.113 uipc_socket2.c
--- sys/kern/uipc_socket2.c     26 Jul 2021 05:51:13 -0000      1.113
+++ sys/kern/uipc_socket2.c     26 Oct 2021 20:49:51 -0000
@@ -212,10 +212,7 @@ soqinsque(struct socket *head, struct so
 {
        soassertlocked(head);
 
-#ifdef DIAGNOSTIC
-       if (so->so_onq != NULL)
-               panic("soqinsque");
-#endif
+       KASSERT(so->so_onq == NULL);
 
        so->so_head = head;
        if (q == 0) {