Merge branch 'act_vlan-allow-modify-zero'

Boris Sukholitko says:

====================
net/sched: act_vlan: Fix modify to allow 0

Currently vlan modification action checks existence of vlan priority by
comparing it to 0. Therefore it is impossible to modify existing vlan
tag to have priority 0.

For example, the following tc command will change the vlan id but will
not affect vlan priority:

tc filter add dev eth1 ingress matchall action vlan modify id 300 \
        priority 0 pipe mirred egress redirect dev eth2

The incoming packet on eth1:

ethertype 802.1Q (0x8100), vlan 200, p 4, ethertype IPv4

will be changed to:

ethertype 802.1Q (0x8100), vlan 300, p 4, ethertype IPv4

although the user has intended to have p == 0.

The fix is to add tcfv_push_prio_exists flag to struct tcf_vlan_params
and rely on it when deciding to set the priority.

The same flag is used to avoid dumping unset vlan priority.

Change Log:
v3 -> v4:
- revert tcf_vlan_get_fill_size change: total size calculation may race vs dump

v2 -> v3:
- Push assumes that the priority is being set
- tcf_vlan_get_fill_size accounts for priority existence

v1 -> v2:
- Do not dump unset priority and fix tests accordingly
- Test for priority 0 modification
====================

Reviewed-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>