We don't need ask_for_local boolean, this is only useful for setup which
can determine the local IP address from the system hostname, which is
probably meaningless for embedded devices (and probably any devices).
It was actually only set by ip_check_options() which is commented out in
lwIP because we don't parse a config file nor check PPP configuration
(user is responsible about writing a configuration which is logical ;-).
Furthermore ask_for_local boolean never set actually had the wrong
default for PPP server setups.
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