8021q: delete cleared egress QoS mappings

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

8021q: delete cleared egress QoS mappings

vlan_dev_set_egress_priority() currently keeps cleared egress

priority mappings in the hash as tombstones. Repeated set/clear cycles

with distinct skb priorities therefore accumulate mapping nodes until

device teardown and leak memory.

Delete mappings when vlan_prio is cleared instead of keeping tombstones.

Now that the egress mapping lists are RCU protected, the node can be

unlinked safely and freed after a grace period.