xsk: Fix fragment node deletion to prevent buffer leak

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

xsk: Fix fragment node deletion to prevent buffer leak

After commit b692bf9a7543 ("xsk: Get rid of xdp_buff_xsk::xskb_list_node"),

the list_node field is reused for both the xskb pool list and the buffer

free list, this causes a buffer leak as described below.

xp_free() checks if a buffer is already on the free list using

list_empty(&xskb->list_node). When list_del() is used to remove a node

from the xskb pool list, it doesn't reinitialize the node pointers.

This means list_empty() will return false even after the node has been

removed, causing xp_free() to incorrectly skip adding the buffer to the

free list.

Fix this by using list_del_init() instead of list_del() in all fragment

handling paths, this ensures the list node is reinitialized after removal,

allowing the list_empty() to work correctly.