net: qrtr: replace qrtr_tx_flow radix_tree with xarray to fix memory leak

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

net: qrtr: replace qrtr_tx_flow radix_tree with xarray to fix memory leak

__radix_tree_create() allocates and links intermediate nodes into the

tree one by one. If a subsequent allocation fails, the already-linked

nodes remain in the tree with no corresponding leaf entry. These orphaned

internal nodes are never reclaimed because radix_tree_for_each_slot()

only visits slots containing leaf values.

The radix_tree API is deprecated in favor of xarray. As suggested by

Matthew Wilcox, migrate qrtr_tx_flow from radix_tree to xarray instead

of fixing the radix_tree itself [1]. xarray properly handles cleanup of

internal nodes — xa_destroy() frees all internal xarray nodes when the

qrtr_node is released, preventing the leak.

[1] https://lore.kernel.org/all/[email protected]/T/