U-Boot version dub-2015.04-r4.5 may report running on Starter Board version 1 even when your Starter Board is version 2.
U-Boot dub-2015.04-r4.5 (Aug 10 2016 - 14:36:02)
CPU: Freescale i.MX6UL rev1.1 528 MHz (running at 396 MHz)
CPU: Industrial temperature grade (-40C to 105C) at 41C
Reset cause: POR
DRAM: 256 MiB
MCA: HW_VER=0.1 FW_VER=0.4
PMIC: PFUZE300 DEV_ID=0x30 REV_ID=0x11
NAND: 256 MiB
MMC: FSL_SDHC: 0
ConnectCore 6UL SOM variant 0x02: Industrial Ultralite 528MHz, 256MB NAND, 256MB DDR3, -40/+85C, Wireless, Bluetooth
Board: ConnectCore 6UL StarterBoard, version 1
Hit any key to stop autoboot: 0
You can tell if your Starter Board is version 2 by looking for the number 30015102-02 on the top-layer screen printing near the CONSOLE/POWER connector.
If your Starter Board is version 2 but U-Boot reports it as version 1, Ethernet does not work in U-Boot.
Download the latest released images of Digi Embedded Yocto and follow the procedure to program the firmware into the device. The latest U-Boot version reports the Starter Board version correctly and Ethernet works normally.
To fix the issue in source code sync your installation with the head of the release branch as follows:
repo init -u https://github.com/digi-embedded/dey-manifest.git -b jethro
repo sync -j4 --no-repo-verify