ath79: mikrotik: fix network setup for lhg-hb platform
This network setup for MikroTik devices based on the LHG-HB platform
avoids using the integrated switch and connects the single Ethernet
port directly. This way, link speed (10/100 Mbps) is properly repor-
ted by eth0.
Fixes: FS#3309
Signed-off-by: Roger Pueyo Centelles <[email protected]>