net/mlx5e: Fix calling wrong function to get inner vlan key and mask

When flow_rule_match_XYZ() functions were first introduced,
flow_rule_match_cvlan() for inner vlan is missing.

In mlx5_core driver, to get inner vlan key and mask, flow_rule_match_vlan()
is just called, which is wrong because it obtains outer vlan information by
FLOW_DISSECTOR_KEY_VLAN.

This commit fixes this by changing to call flow_rule_match_cvlan() after
it's added.

Fixes: 8f256622 ("flow_offload: add flow_rule and flow_match structures and use them")
Signed-off-by: Jianbo Liu <jianbol@mellanox.com>
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>