I'm seeing series of e1000e resets (sometimes endless) at system boot
if something generates tx traffic at this time. In my case this is
netconsole who sends message "e1000e 0000:02:00.0: Some CPU C-states
have been disabled in order to enable jumbo frames" from e1000e itself.
As result e1000_watchdog_task sees used tx buffer while carrier is off
and start this reset cycle again.

[   17.794359] e1000e: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[   17.794714] IPv6: ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
[   22.936455] e1000e 0000:02:00.0 eth1: changing MTU from 1500 to 9000
[   23.033336] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   26.102364] e1000e: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[   27.174495] 8021q: 802.1Q VLAN Support v1.8
[   27.174513] 8021q: adding VLAN 0 to HW filter on device eth1
[   30.671724] cgroup: cgroup: disabling cgroup2 socket matching due to net_prio or net_cls activation
[   30.898564] netpoll: netconsole: local port 6666
[   30.898566] netpoll: netconsole: local IPv6 address 2a02:6b8:0:80b:beae:c5ff:fe28:23f8
[   30.898567] netpoll: netconsole: interface 'eth1'
[   30.898568] netpoll: netconsole: remote port 6666
[   30.898568] netpoll: netconsole: remote IPv6 address 2a02:6b8:b000:605c:e61d:2dff:fe03:3790
[   30.898569] netpoll: netconsole: remote ethernet address b0:a8:6e:f4:ff:c0
[   30.917747] console [netcon0] enabled
[   30.917749] netconsole: network logging started
[   31.453353] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.185730] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.321840] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.465822] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.597423] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.745417] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   34.877356] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   35.005441] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   35.157376] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   35.289362] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   35.417441] e1000e 0000:02:00.0: Some CPU C-states have been disabled in order to enable jumbo frames
[   37.790342] e1000e: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None

This patch flushes tx buffers only once when carrier is off
rather than at each watchdog iteration.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>