dpll: align help and man notation with actual option parsing

dpll: align help and man notation with actual option parsing

dpll uses getopt_long(), which only accepts long options with the
"--" prefix.  The iproute2-wide "-X[name]" shorthand used in the
help text and man page implies a single-dash long form
(e.g. -Version, -json, -pretty) that getopt_long does not parse;
only -V/--Version, -j/--json and -p/--pretty actually work.

Replace the misleading shorthand with explicit "-V | --Version"
style so the documented forms match what the parser accepts, and
drop the redundant second usage line in help() that listed only a
subset of the options and implied dpll could be invoked without an
OBJECT.  No functional change.

Signed-off-by: Petr Oros <poros@redhat.com>
Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>