net/sched: ets: fix divide by zero in the offload path

In the Linux kernel, the following vulnerability has been resolved:

net/sched: ets: fix divide by zero in the offload path

Offloading ETS requires computing each class' WRR weight: this is done by
averaging over the sums of quanta as 'q_sum' and 'q_psum'. Using unsigned
int, the same integer size as the individual DRR quanta, can overflow and
even cause division by zero, like it happened in the following splat:

Oops: divide error: 0000 [#1] SMP PTI
CPU: 13 UID: 0 PID: 487 Comm: tc Tainted: G E 6.19.0-virtme #45 PREEMPT(full)
Tainted: [E]=UNSIGNED_MODULE
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
RIP: 0010:ets_offload_change+0x11f/0x290 [sch_ets]
Code: e4 45 31 ff eb 03 41 89 c7 41 89 cb 89 ce 83 f9 0f 0f 87 b7 00 00 00 45 8b 08 31 c0 45 01 cc 45 85 c9 74 09 41 6b c4 64 31 d2 <41> f7 f2 89 c2 44 29 fa 45 89 df 41 83 fb 0f 0f 87 c7 00 00 00 44
RSP: 0018:ffffd0a180d77588 EFLAGS: 00010246
RAX: 00000000ffffff38 RBX: ffff8d3d482ca000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffd0a180d77660
RBP: ffffd0a180d77690 R08: ffff8d3d482ca2d8 R09: 00000000fffffffe
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000fffffffe
R13: ffff8d3d472f2000 R14: 0000000000000003 R15: 0000000000000000
FS: 00007f440b6c2740(0000) GS:ffff8d3dc9803000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000003cdd2000 CR3: 0000000007b58002 CR4: 0000000000172ef0
Call Trace:
<TASK>
ets_qdisc_change+0x870/0xf40 [sch_ets]
qdisc_create+0x12b/0x540
tc_modify_qdisc+0x6d7/0xbd0
rtnetlink_rcv_msg+0x168/0x6b0
netlink_rcv_skb+0x5c/0x110
netlink_unicast+0x1d6/0x2b0
netlink_sendmsg+0x22e/0x470
____sys_sendmsg+0x38a/0x3c0
___sys_sendmsg+0x99/0xe0
__sys_sendmsg+0x8a/0xf0
do_syscall_64+0x111/0xf80
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f440b81c77e
Code: 4d 89 d8 e8 d4 bc 00 00 4c 8b 5d f8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 11 c9 c3 0f 1f 80 00 00 00 00 48 8b 45 10 0f 05 <c9> c3 83 e2 39 83 fa 08 75 e7 e8 13 ff ff ff 0f 1f 00 f3 0f 1e fa
RSP: 002b:00007fff951e4c10 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000481820 RCX: 00007f440b81c77e
RDX: 0000000000000000 RSI: 00007fff951e4cd0 RDI: 0000000000000003
RBP: 00007fff951e4c20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff951f4fa8
R13: 00000000699ddede R14: 00007f440bb01000 R15: 0000000000486980
</TASK>
Modules linked in: sch_ets(E) netdevsim(E)
---[ end trace 0000000000000000 ]---
RIP: 0010:ets_offload_change+0x11f/0x290 [sch_ets]
Code: e4 45 31 ff eb 03 41 89 c7 41 89 cb 89 ce 83 f9 0f 0f 87 b7 00 00 00 45 8b 08 31 c0 45 01 cc 45 85 c9 74 09 41 6b c4 64 31 d2 <41> f7 f2 89 c2 44 29 fa 45 89 df 41 83 fb 0f 0f 87 c7 00 00 00 44
RSP: 0018:ffffd0a180d77588 EFLAGS: 00010246
RAX: 00000000ffffff38 RBX: ffff8d3d482ca000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffd0a180d77660
RBP: ffffd0a180d77690 R08: ffff8d3d482ca2d8 R09: 00000000fffffffe
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000fffffffe
R13: ffff8d3d472f2000 R14: 0000000000000003 R15: 0000000000000000
FS: 00007f440b6c2740(0000) GS:ffff8d3dc9803000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000003cdd2000 CR3: 0000000007b58002 CR4: 0000000000172ef0
Kernel panic - not syncing: Fatal exception
Kernel Offset: 0x30000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
---[ end Kernel panic - not syncing: Fatal exception ]---

Fix this using 64-bit integers for 'q_sum' and 'q_psum'.