Until now, the main function of the sandbox port wants to use the libc
getopt(), but as we have a getopt() implementation in barebox as well,
it is silently used instead. This works in the usual case, but if an
error occurs (i.e. by using an unknown argument) in getopt(), the
implementation tries to write to the console, which is not initialized
and thus breaks with a null pointer exception.

This patch changes the main function to use getopt_long() instead of
getopt(). This makes us use the implementation in glibc and while being
there, we get long options, which makes us look more professional...

Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>