CVE-2026-98285: net: bridge: vlan: fix bugs caused by switchdev deletion errors

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

net: bridge: vlan: fix bugs caused by switchdev deletion errors

Allowing switchdev to prevent vlan deletion and error out in vlandel could cause multiple different issues - inconsistent state, memory leaks when flushing, NULL pointer dereference on bridge error when flushing. It doesn't make sense to allow it to stop vlandel, so log the error and continue with software vlan deletion. This is also consistent with 8021q behaviour.