ipn/ipnlocal: disable sockstats on (unstable) mobile by default

We're tracking down a new instance of memory usage, and excessive memory usage
from sockstats is definitely not going to help with debugging, so disable it by
default on mobile.

Updates tailscale/corp#18514

Signed-off-by: James Tucker <james@tailscale.com>

ipn/ipnlocal/local.go

@@ -405,8 +405,8 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 	if err != nil {
 		log.Printf("error setting up sockstat logger: %v", err)
 	}
-	// Enable sockstats logs only on unstable builds
-	if version.IsUnstableBuild() && b.sockstatLogger != nil {
+	// Enable sockstats logs only on non-mobile unstable builds
+	if version.IsUnstableBuild() && !version.IsMobile() && b.sockstatLogger != nil {
 		b.sockstatLogger.SetLoggingEnabled(true)
 	}