webrtc: add NAT1To1IPs []string to Config for multi-IP support (issue #20)

core/webrtc/config.go

@@ -17,8 +17,18 @@ type Config struct {
 
 	// PublicIP is the server's externally-reachable IP, advertised in ICE
 	// candidates via NAT1To1. Empty means rely on STUN discovery.
+	// Deprecated in favour of NAT1To1IPs for multi-homed servers; when both
+	// are set, PublicIP is treated as the first entry in NAT1To1IPs.
 	PublicIP string
 
+	// NAT1To1IPs is the list of NAT1To1 IPs for ICE host candidates.
+	// When non-empty, Pion advertises a host candidate for each IP so that
+	// peers can reach this server through NAT on any of the listed addresses.
+	// Takes precedence over PublicIP when set; PublicIP is treated as a member
+	// of this list when both are configured. Typical use: dual-homed servers
+	// with both a LAN IP and a public IP.
+	NAT1To1IPs []string
+
 	// UDPPortRange bounds the local UDP ports allocated for FFmpeg→Pion RTP.
 	UDPPortRange PortRange
 
@@ -35,6 +45,7 @@ func DefaultConfig() Config {
 		Enabled:       true,
 		WHEPListen:    ":8787",
 		PublicIP:      "",
+		NAT1To1IPs:    nil,
 		UDPPortRange:  PortRange{Low: 10000, High: 10100},
 		ICEServers:    []string{"stun:stun.cloudflare.com:3478", "stun:stun.l.google.com:19302"},
 		MaxPeersTotal: 32,