switch to new sync/atomic helpers in go1.19 (#728)

These new helpers make the code a lot cleaner. I confirmed that the
simple helpers like `atomic.Int64` don't add any extra overhead as they
get inlined by the compiler. `atomic.Pointer` adds an extra method call
as it no longer gets inlined, but we aren't using these on the hot path
so it is probably okay.

inside.go

@@ -1,8 +1,6 @@
 package nebula
 
 import (
-	"sync/atomic"
-
 	"github.com/flynn/noise"
 	"github.com/sirupsen/logrus"
 	"github.com/slackhq/nebula/firewall"
@@ -222,7 +220,7 @@ func (f *Interface) SendVia(viaIfc interface{},
 ) {
 	via := viaIfc.(*HostInfo)
 	relay := relayIfc.(*Relay)
-	c := atomic.AddUint64(&via.ConnectionState.atomicMessageCounter, 1)
+	c := via.ConnectionState.messageCounter.Add(1)
 
 	out = header.Encode(out, header.Version, header.Message, header.MessageRelay, relay.RemoteIndex, c)
 	f.connectionManager.Out(via.vpnIp)
@@ -281,7 +279,7 @@ func (f *Interface) sendNoMetrics(t header.MessageType, st header.MessageSubType
 
 	//TODO: enable if we do more than 1 tun queue
 	//ci.writeLock.Lock()
-	c := atomic.AddUint64(&ci.atomicMessageCounter, 1)
+	c := ci.messageCounter.Add(1)
 
 	//l.WithField("trace", string(debug.Stack())).Error("out Header ", &Header{Version, t, st, 0, hostinfo.remoteIndexId, c}, p)
 	out = header.Encode(out, header.Version, t, st, hostinfo.remoteIndexId, c)