CVE-2026-72246: netfilter: flowtable: use correct direction to set up tunnel route

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

netfilter: flowtable: use correct direction to set up tunnel route

The layer 2 encapsulation and layer 3 tunnel information in the xmit path is taken from the other tuple, because the tunnel information that is included in the tuple for hashtable lookups is also used to perform the egress encapsulation in the transmit path.

This patch uses the correct direction when setting up the tunnel, the original proposed patch to address this fix uses the reversed direction.

While at it, remove the redundant check to call dstrelease() to drop the reference on the dst that was obtained from the forward path, which is not useful in the direct xmit path unless tunneling is performed.