[BUG] dhcp fails to download file with CONFIG_NET_LWIP=y

[Heinrich Schuchardt]

Hello Jerome,

Using the old network stack U-Boot's dhcp command can be used to 
download via TFTP. This fails with the lwIP stack:

StarFive # dhcp $kernel_addr_r 192.168.1.103:/vf2/grubriscv64.efi
ethernet at 16030000 Waiting for PHY auto negotiation to complete.... done
DHCP client bound to address 192.168.1.47 (233 ms)
StarFive # tftpboot $kernel_addr_r 192.168.1.103:/vf2/grubriscv64.efi
Using ethernet at 16030000 device
TFTP from server 192.168.1.103; our IP address is 192.168.1.47
Filename '/vf2/grubriscv64.efi'.
Load address: 0x40200000
Loading: #################################################################
          #################################################################
          #################################################################
          #################################################################
          #########
          4.1 MiB/s

We should try to provide the old functionality to make the move to lwIP 
seamless.

In the CI QEMU instances we already have

test/py/tests/test_net.py

to test tftpboot. We should add an equivalent dhcp test.

Best regards

Heinrich