stats: Report group indices as unsigned int

Currently the unsigned group index value is silently being cast to
(signed) int in the log and statsd reporter code. If the resulting
value is negative (which can happen for instance with MMCTX
counters), the index is assumed to be unset.

This commit changes the affected types to unsigned. The index value 0
is then the only value indicating an unset group.

Sponsored-by: On-Waves ehf
1 file changed