It seems that the issue from version 7.0 still exists in version 7.1. When nothing is connected, some of the GBE interfaces show ‘yes’.
root@tegra-ubuntu:/home/tj_software# for iface in /sys/class/net/mgbe*; do ethtool $(basename $iface) | grep "Link detected"; done
Link detected: yes
Link detected: yes
Link detected: yes
Link detected: no