[BUG] Strange vlan handling on e1000e

[BUG] Strange vlan handling on e1000e

[Armin Wolf]

When using a Python script to send max sized vlan packets
on a BCM4401 nic (driver: b44), the Intel I217-V nic (driver: e1000e) only
receives packets with a maximum size of 1514 bytes and reports a
length error for the 1518 bytes sized packet.

When sending the packet from the I217-V and receiving with
the BCM4401 however, both packets are received without errors.

This still happens when both sides are directly connected
thru a single ethernet cable.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212613

hostnamectl | grep "Operating System":
  Operating System: Debian GNU/Linux 10 (buster)

Kernel version I217-V: 5.12.0-rc4 (net-next)
Kernel version BCM4401: 4.19.0-181

Python script:

from scapy.all import *

pkg1 = Ether(dst="FF:FF:FF:FF:FF:FF")/Dot1Q(vlan=100, type=0x8000)/Raw(load=b"\xFF" * 1500)
print("1st lenght: " + str(len(pkg1)) + " Byte + 4 Byte FCS")
sendp(pkg1, iface="eth0.100")

pkg2 = Ether(dst="FF:FF:FF:FF:FF:FF")/Dot1Q(vlan=100, type=0x8000)/Raw(load=b"\xFF" * 1496)
print("2nd lenght: " + str(len(pkg2)) + " Byte + 4 Byte FCS")
sendp(pkg2, iface="eth0.100")