Recover support for X540_BYPASS cards

Hi,

Some time ago I've found out myself a way to end up having at home a X540-T2 (copper) card with a set of relays on it that allows to enable a "bypass" mode, in which both ethernet ports gets physically connected between them bypassing the NIC.

However, its PCI device ID (0x155C) is not included on the list of supported devices for this driver. Not only that, but after some research, I've found that it _used_ to be supported in the mainline kernel and it was removed from the device list because the bypass ids where "unused" ([ref](https://lore.kernel.org/all/20180910163753.85966-3-xiaoyun.li@intel.com/)).

I've been using this card for months with a custom build of the ixgbe driver including its device ID without problems, so I'm really curious about why it was removed in the first place.

Is there any possibility of recovering this device ID in both this repository and in the mainline kernel? It would be quite convenient to not need to make a fork of this repository or rebuild the kernel in order to have this device working (even without bypass functions).

Thanks in advance.