rose: fix dangling neighbour pointers in rose_rt_device_down()

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

rose: fix dangling neighbour pointers in rose_rt_device_down()

There are two bugs in rose_rt_device_down() that can cause

use-after-free:

1. The loop bound `t->count` is modified within the loop, which can

cause the loop to terminate early and miss some entries.

2. When removing an entry from the neighbour array, the subsequent entries

are moved up to fill the gap, but the loop index `i` is still

incremented, causing the next entry to be skipped.

For example, if a node has three neighbours (A, A, B) with count=3 and A

is being removed, the second A is not checked.

i=0: (A, A, B) -> (A, B) with count=2

^ checked

i=1: (A, B) -> (A, B) with count=2

^ checked (B, not A!)

i=2: (doesn't occur because i < count is false)

This leaves the second A in the array with count=2, but the rose_neigh

structure has been freed. Code that accesses these entries assumes that

the first `count` entries are valid pointers, causing a use-after-free

when it accesses the dangling pointer.

Fix both issues by iterating over the array in reverse order with a fixed

loop bound. This ensures that all entries are examined and that the removal

of an entry doesn't affect subsequent iterations.