setpriv: do not process remaining args

setpriv: do not process remaining args

By default, the 'getopt32' call will continue parsing the command line
even after hitting a non-option string. But in setpriv, this should be
avoided, as all parameters following the initial non-option argument are
in fact arguments to the binary that is to be executed by setpriv.
Otherwise, calling e.g. 'busybox setpriv ls -l' would result in an error
due to the unknown parameter "-l".

Fix the issue by passing "+" as the first character in the options
string. This will cause 'getopt32' to stop processing after hitting the
first non-option.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>