net: lwip: dhcp: support arguments for TFTP file download

The dhcp command is supposed to have the following syntax as per
"help dhcp":

  dhcp [loadAddress] [[hostIPaddr:]bootfilename]

In other words, any arguments should be passed to an implicit
tftpboot command after the DHCP exchange has occurred.

Add the missing code to the lwIP version of do_dhcp().

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
1 file changed