ipn: add sockstat logger to stable builds

This makes the sockstat logger available on all builds, but only enables
it by default for unstable.  For stable builds, the logger must be
explicitly enabled via C2N component logger.

Updates tailscale/corp#9230
Updates #3363

Signed-off-by: Will Norris <will@tailscale.com>

ipn/ipnlocal/local.go

@@ -313,16 +313,14 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, store ipn.StateStor
 		loginFlags:     loginFlags,
 	}
 
-	// for now, only log sockstats on unstable builds
-	if version.IsUnstableBuild() {
 	b.sockstatLogger, err = sockstatlog.NewLogger(logpolicy.LogsDir(logf), logf, logID)
 	if err != nil {
 		log.Printf("error setting up sockstat logger: %v", err)
 	}
-		if b.sockstatLogger != nil {
+	// Enable sockstats logs only on unstable builds
+	if version.IsUnstableBuild() && b.sockstatLogger != nil {
 		b.sockstatLogger.SetLoggingEnabled(true)
 	}
-	}
 
 	// Default filter blocks everything and logs nothing, until Start() is called.
 	b.setFilter(filter.NewAllowNone(logf, &netipx.IPSet{}))