stats: Fix not reported stat item values

Currently the global stat item index is being advanced in
osmo_stat_item_group_handler, so that the second and further groups
in the list will skip new item values.

This commit moves the call to osmo_stat_item_discard_all into
osmo_stats_report to a place where all groups have been processed
already.

Sponsored-by: On-Waves ehf
1 file changed