Fix: set SO_REUSEADDR for UDP listeners on linux (#630)

dns/server.go

@@ -3,6 +3,8 @@ package dns
 import (
 	"net"
 
+	"github.com/Dreamacro/clash/common/sockopt"
+
 	D "github.com/miekg/dns"
 )
 
@@ -58,6 +60,11 @@ func ReCreateServer(addr string, resolver *Resolver) error {
 		return err
 	}
 
+	err = sockopt.UDPReuseaddr(p)
+	if err != nil {
+		return err
+	}
+
 	address = addr
 	handler := newHandler(resolver)
 	server = &Server{handler: handler}