ipn/ipnlocal: log number of packet filters rather than entire filter

The number of packet filters can grow very large,
so this log entry can be very large.
We can get the packet filter server-side,
so reduce verbosity here to just the number of filters present.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

ipn/ipnlocal/local.go

@@ -961,7 +961,7 @@ func (b *LocalBackend) updateFilter(netMap *netmap.NetworkMap, prefs *ipn.Prefs)
 		b.logf("netmap packet filter: (shields up)")
 		b.e.SetFilter(filter.NewShieldsUpFilter(localNets, logNets, oldFilter, b.logf))
 	} else {
-		b.logf("netmap packet filter: %v", packetFilter)
+		b.logf("netmap packet filter: %v filters", len(packetFilter))
 		b.e.SetFilter(filter.New(packetFilter, localNets, logNets, oldFilter, b.logf))
 	}
 }