Hi Vladimir, I've some problem bringing up the on board Flash on my board, so can not test booting uImage without using eth before it's fixed.
In the env ramboot, uboot do something to set up the network, by command adipp, Did you do the same after kernel booting up? Have you tried setting the equivalent value as u-boot addip would do, then 1) ifconfig eth0 down, 2)ifconfig eth0 up ?