fff-hoods: Fix case of missing keyxchangev2data

This fixes a missing /tmp/keyxchangev2data due to gateway
misconfiguration.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Tim Niemeyer <tim@tn-x.org>
- Added double quote around $jsonfile
Signed-off-by: Tim Niemeyer <tim@tn-x.org>