Rework some things into packages (#489)

udp/conn.go

@@ -0,0 +1,20 @@
+package udp
+
+import (
+	"github.com/slackhq/nebula/firewall"
+	"github.com/slackhq/nebula/header"
+)
+
+const MTU = 9001
+
+type EncReader func(
+	addr *Addr,
+	out []byte,
+	packet []byte,
+	header *header.H,
+	fwPacket *firewall.Packet,
+	lhh LightHouseHandlerFunc,
+	nb []byte,
+	q int,
+	localCache firewall.ConntrackCache,
+)