net: lwip: add wget command

net: lwip: add wget command

Add support for the wget command with NET_LWIP. The command normally
expects a URL: wget [loadaddr] url, but it also accepts the legacy
syntax: wget [loadaddr] [server:]file.
The server IP may alternatively be supplied via ${httpserverip} which
has higher priority than ${serverip}.

Based on code initially developed by Maxim U.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Co-developed-by: Maxim Uvarov <muvarov@gmail.com>
Cc: Maxim Uvarov <muvarov@gmail.com>
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>