igc: Check VLAN TCI mask

Currently the driver accepts VLAN TCI steering rules regardless of the
configured mask. And things might fail silently or with confusing error
messages to the user.

There are two ways to handle the VLAN TCI mask:

 1. Match on the PCP field using a VLAN prio filter
 2. Match on complete TCI field using a flex filter

Therefore, add checks and code for that.

For instance the following rule is invalid and will be converted into a
VLAN prio rule which is not correct:
|root@host:~# ethtool -N enp3s0 flow-type ether vlan 0x0001 m 0xf000 \
|             action 1
|Added rule with ID 61
|root@host:~# ethtool --show-ntuple enp3s0
|4 RX rings available
|Total 1 rules
|
|Filter: 61
|        Flow Type: Raw Ethernet
|        Src MAC addr: 00:00:00:00:00:00 mask: FF:FF:FF:FF:FF:FF
|        Dest MAC addr: 00:00:00:00:00:00 mask: FF:FF:FF:FF:FF:FF
|        Ethertype: 0x0 mask: 0xFFFF
|        VLAN EtherType: 0x0 mask: 0xffff
|        VLAN: 0x1 mask: 0x1fff
|        User-defined: 0x0 mask: 0xffffffffffffffff
|        Action: Direct to queue 1

After:
|root@host:~# ethtool -N enp3s0 flow-type ether vlan 0x0001 m 0xf000 \
|             action 1
|rmgr: Cannot insert RX class rule: Operation not supported

Fixes: 7991487e

 ("igc: Allow for Flex Filters to be installed")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>