uboot-imx

net: Re-check prerequisites when autoloading

With net autoload, we check the prerequisites for the initial command,
but the greater prerequisites when autoloading are not checked.

If we would attempt to autoload, check those prerequisites too.

If we are not expecting a serverip from the server, then don't worry
about it not being set, but don't attempt to load if it isn't.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>