lwIP watchdog not being serviced

[Tim Harvey]

Hi Jerome,

In my continued evaluation to see if I want to switch my boards over
to use lwIP I've noticed that the watchdog does not get serviced
during at least http/tftp which surprised me. This causes board resets
when transferring large files such as disk images.

It seems lwIP is missing some calls to schedule(). Do you have a
suggestion for the right place to call this for lwIP?

Best Regards,

Tim