fix(netstat): enable curated stats for tcp connections (#1004)

Reduce cardinality of `tcp_connection_stats` by only keeping curated
stats. Updates curated stats to include:
- timeouts
- loss probes
- loss retransmit

Curation was off, but there were already several curated stats for drops
and errors.

### Testing

I only see these stats after this change:

```
networkobservability_tcp_connection_stats{statistic_name="TCPLossProbes"} 233948
networkobservability_tcp_connection_stats{statistic_name="TCPLostRetransmit"} 143
networkobservability_tcp_connection_stats{statistic_name="TCPTimeouts"} 240
```

In a steady state cluster, the first stat seems to slowly increase over
time, and the other two are constant.

Signed-off-by: Hunter Gregory <[email protected]>

pkg/plugin/linuxutil/linuxutil_linux.go

@@ -67,7 +67,7 @@ func (lu *linuxUtil) run(ctx context.Context) error {
 			return nil
 		case <-ticker.C:
 			opts := &NetstatOpts{
-				CuratedKeys:      false,
+				CuratedKeys:      true,
 				AddZeroVal:       false,
 				ListenSock:       false,
 				PrevTCPSockStats: lu.prevTCPSockStats,

pkg/plugin/linuxutil/types_linux.go

@@ -35,6 +35,9 @@ var netstatCuratedKeys = map[string]struct{}{
 	"DataCsumErr":        {},
 	"AddAddrDrop":        {},
 	"RmAddrDrop":         {},
+	"TCPTimeouts": 	      {},
+	"TCPLossProbes":      {},
+	"TCPLostRetransmit":  {},
 }
 
 type ConnectionStats struct {