lan discovery will be done soon

Signed-off-by: fufesou <shuanglongchen@yeah.net>

libs/hbb_common/protos/discovery.proto

@@ -8,3 +8,8 @@ message Discovery {
   /// response port for current listening port(udp for now)
   int32 port = 2;
 }
+
+message DiscoveryBack {
+  string id = 1;
+  base.PeerInfo peer = 2;
+}

libs/hbb_common/src/config.rs

@@ -55,6 +55,8 @@ pub const RENDEZVOUS_SERVERS: &'static [&'static str] = &[
 pub const RENDEZVOUS_PORT: i32 = 21116;
 pub const RELAY_PORT: i32 = 21117;
 
+pub const SERVER_UDP_PORT: u16 = 21001; // udp
+
 #[derive(Debug, Default, Serialize, Deserialize, Clone)]
 pub struct Config {
     #[serde(default)]