Lighthouse handler optimizations (#320)

We noticed that the number of memory allocations LightHouse.HandleRequest creates for each call can seriously impact performance for high traffic lighthouses. This PR introduces a benchmark in the first commit and then optimizes memory usage by creating a LightHouseHandler struct. This struct allows us to re-use memory between each lighthouse request (one instance per UDP listener go-routine).

udp_generic.go

@@ -108,6 +108,8 @@ func (u *udpConn) ListenOut(f *Interface) {
 	udpAddr := &udpAddr{}
 	nb := make([]byte, 12, 12)
 
+	lhh := f.lightHouse.NewRequestHandler()
+
 	for {
 		// Just read one packet at a time
 		n, rua, err := u.ReadFromUDP(buffer)
@@ -117,7 +119,7 @@ func (u *udpConn) ListenOut(f *Interface) {
 		}
 
 		udpAddr.UDPAddr = *rua
-		f.readOutsidePackets(udpAddr, plaintext[:0], buffer[:n], header, fwPacket, nb)
+		f.readOutsidePackets(udpAddr, plaintext[:0], buffer[:n], header, fwPacket, lhh, nb)
 	}
 }