Looking at the 5.6 kernel source (2.6.18-238), the file drivers/net/ixgbe/ixgbe_type.h has the line:
#define IXGBE_DEV_ID_82599_T3_LOM 0x151C
which part of the patch:
linux-2.6-net-ixgbe-update-to-upstream-version-2-0-84-k2.patch
I'll need to test it once available, but may prefer to stick to the newer Intel driver (until 5.7 at least :)
Thanks!