support/download/dl-wrapper: fix passing remaining options to helper scripts

support/download/dl-wrapper: fix passing remaining options to helper scripts

When calling the backend-specific helper scripts, the remaining
options are in ${@}. However, in order to let the helper script know
that those remaining options should not be parsed, but instead passed
as-is to the download tool, they must be separated from the main
options by "--".

Without this, packages that use <pkg>_DL_OPTS, such as the
amd-catalyst package, cannot download their tarball anymore.

Fixes:

  http://autobuild.buildroot.net/results/de818f6e4c8e63d5e8a49c445d10c34eccc40410/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>