Add more metrics (#450)

* Add more metrics

This change adds the following counter metrics:

Metrics to track packets dropped at the firewall:

    firewall.dropped.local_ip
    firewall.dropped.remote_ip
    firewall.dropped.no_rule

Metrics to track handshakes attempts that have been initiated and ones
that have timed out (ones that have completed are tracked by the
existing "handshakes" histogram).

    handshake_manager.initiated
    handshake_manager.timed_out

Metrics to track when cached_packets are dropped because we run out of
buffer space, and how many are sent once the handshake completes.

    hostinfo.cached_packets.dropped
    hostinfo.cached_packets.sent

This change also notes how many cached packets we have when we log the
final "Handshake received" message for either stage1 for stage2.

* separate incoming/outgoing metrics

* remove "allowed" firewall metrics

We don't need this on the hotpath, they aren't worh it.

* don't need pointers here

inside.go

@@ -45,7 +45,7 @@ func (f *Interface) consumeInsidePacket(packet []byte, fwPacket *FirewallPacket,
 		// the packet queue.
 		ci.queueLock.Lock()
 		if !ci.ready {
-			hostinfo.cachePacket(f.l, message, 0, packet, f.sendMessageNow)
+			hostinfo.cachePacket(f.l, message, 0, packet, f.sendMessageNow, f.cachedPacketMetrics)
 			ci.queueLock.Unlock()
 			return
 		}
@@ -164,7 +164,7 @@ func (f *Interface) SendMessageToVpnIp(t NebulaMessageType, st NebulaMessageSubT
 		// the packet queue.
 		hostInfo.ConnectionState.queueLock.Lock()
 		if !hostInfo.ConnectionState.ready {
-			hostInfo.cachePacket(f.l, t, st, p, f.sendMessageToVpnIp)
+			hostInfo.cachePacket(f.l, t, st, p, f.sendMessageToVpnIp, f.cachedPacketMetrics)
 			hostInfo.ConnectionState.queueLock.Unlock()
 			return
 		}