Fix WebRTC server with static UDP port

pkg/net2/net.go

@@ -0,0 +1,32 @@
+package net2
+
+import (
+	"net"
+	"strconv"
+)
+
+// Docker has common docker addresses (class B):
+// https://en.wikipedia.org/wiki/Private_network
+// - docker0 172.17.0.1/16
+// - br-xxxx 172.18.0.1/16
+// - hassio  172.30.32.1/23
+var Docker = net.IPNet{
+	IP:   []byte{172, 16, 0, 0},
+	Mask: []byte{255, 240, 0, 0},
+}
+
+// ParseUnspecifiedPort will return port if address is unspecified
+// ex. ":8555" or "0.0.0.0:8555"
+func ParseUnspecifiedPort(address string) int {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		return 0
+	}
+
+	if host != "" && host != "0.0.0.0" && host != "[::]" {
+		return 0
+	}
+
+	i, _ := strconv.Atoi(port)
+	return i
+}