igc: Add TransmissionOverrun counter

igc: Add TransmissionOverrun counter

Add TransmissionOverrun as per defined by IEEE 802.1Q Bridges.
TransmissionOverrun counter shall be incremented if the implementation
detects that a frame from a given queue is still being transmitted by
the MAC when that gate-close event for that queue occurs.

This counter is utilised by the Certification conformance test to
inform the user application whether any packets are currently being
transmitted on a particular queue during a gate-close event.

Intel Discrete I225/I226 have a mechanism to not transmit a packets if
the gate open time is insufficient for the packet transmission by setting
the Strict_End bit. Thus, it is expected for this counter to be always
zero at this moment.

Inspired from enetc_taprio_stats() and enetc_taprio_queue_stats(), now
driver also report the tx_overruns counter per traffic class.

User can get this counter by using below command:
1) tc -s qdisc show dev <interface> root
2) tc -s class show dev <interface>

Test Result (Before):
class mq :1 root
 Sent 1289 bytes 20 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :2 root
 Sent 124 bytes 2 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :3 root
 Sent 46028 bytes 86 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :4 root
 Sent 2596 bytes 14 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0

Test Result (After):
class taprio 100:1 root
 Sent 8491 bytes 38 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 Transmit overruns: 0
class taprio 100:2 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 Transmit overruns: 0
class taprio 100:3 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
 Transmit overruns: 0
class taprio 100:4 root
 Sent 994 bytes 11 pkt (dropped 0, overlimits 0 requeues 1)
 backlog 0b 0p requeues 1
 Transmit overruns: 0

Signed-off-by: Muhammad Husaini Zulkifli <[email protected]>
Reviewed-by: Vladimir Oltean <[email protected]>
Tested-by: Naama Meir <[email protected]>
Signed-off-by: Tony Nguyen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>