pimd: Add additional IGMP stats (peak number of groups)

```
exit1-debian-11# sh ip igmp statistics interface eth2
IGMP statistics
Interface            : eth2
V1 query             : 0
V2 query             : 0
V3 query             : 25
V2 leave             : 0
V1 report            : 0
V2 report            : 0
V3 report            : 34
mtrace response      : 0
mtrace request       : 0
unsupported          : 0
joins failed         : 0
joins sent           : 13
general queries sent : 2
group queries sent   : 24
peak groups          : 9
total groups         : 4
total source groups  : 1
exit1-debian-11# sh ip igmp statistics interface eth2 json
{
  "eth2":{
    "name":"eth2",
    "queryV1":0,
    "queryV2":0,
    "queryV3":25,
    "leaveV2":0,
    "reportV1":0,
    "reportV2":0,
    "reportV3":34,
    "mtraceResponse":0,
    "mtraceRequest":0,
    "unsupported":0,
    "peakGroups":9,
    "totalGroups":4,
    "totalSourceGroups":1,
    "joinsFailed":0,
    "joinsSent":13,
    "generalQueriesSent":2,
    "groupQueriesSent":24
  }
}
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/pimd/pim_igmp_stats.c b/pimd/pim_igmp_stats.c
index 6a5ce4dc8d..1d51104687 100644
--- a/pimd/pim_igmp_stats.c
+++ b/pimd/pim_igmp_stats.c
@@ -43,6 +43,7 @@ void igmp_stats_add(struct igmp_stats *a, struct igmp_stats *b)
 	a->mtrace_rsp += b->mtrace_rsp;
 	a->mtrace_req += b->mtrace_req;
 	a->unsupported += b->unsupported;
+	a->peak_groups += b->peak_groups;
 	a->total_groups += b->total_groups;
 	a->total_source_groups += b->total_source_groups;
 	a->joins_sent += b->joins_sent;