ARC: fix ethernet operation with another MAC-address
 * dhcp now works
 * 100 Mbit auto-negotiated connection works

For some reason fake MAC address 11:22:33:44:55:66 lead to completely
unexpected behavior of networking:
 * auto-negotiated 100 Mbit connection was non-functional
 * in some networks even manually set 10/100 Mbit connection didn't work
 
With any different MAC address (I took here the one from HAPS/ml-50x
config proposed by Frank back in the day) networking works flawlessly.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>