ipq806x: Stabilize LAN 2 MAC address, interface ordering

ipq806x: Stabilize LAN 2 MAC address, interface ordering

Part 1 of #13629 split.

* Sets the LAN 2 MAC address in the DTS by deriving it from LAN 1's
address. The factory OS derives this from the `eth1addr` u-boot env
variable, but the nvmem_u-boot-env driver doesn't support parsing MAC
addresses from fields other than `ethaddr`. But for all of the device
samples I've checked (~10) it derives the correct MAC.

* Updates 02_network to ensure that interfaces are assigned to roles
correctly and consistently.

Signed-off-by: Bryan Berg <bdb@north-eastham.org>