ionic: move filter sync_needed bit set

Move the setting of the filter-sync-needed bit to the error
case in the filter add routine to be sure we're checking the
live filter status rather than a copy of the pre-sync status.

Fixes: 969f8439 ("ionic: sync the filters in the work task")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>