always use SO_REUSEADDR and deprecate the flag to turn it on

ChangeLog

@@ -1,5 +1,6 @@
 	* fix nagle implementation in uTP
 
+	* always use SO_REUSEADDR and deprecate the flag to turn it on
 	* add python bindings for SSL support
 	* minor uTP tweaks
 	* fix end-game mode issue when some files are selected to not be downloaded

include/libtorrent/session.hpp

@@ -329,7 +329,10 @@ namespace libtorrent
 		// the error. It will return true on success.
 		enum listen_on_flags_t
 		{
+#ifndef TORRENT_NO_DEPRECATE
+			// this is always on starting with 0.16.2
 			listen_reuse_address = 0x01,
+#endif
 			listen_no_system_port = 0x02
 		};
 

src/session_impl.cpp

@@ -2083,11 +2083,10 @@ namespace aux {
 #endif
 			return;
 		}
-		if (flags & session::listen_reuse_address)
-		{
-			error_code err; // ignore errors here
-			s->sock->set_option(socket_acceptor::reuse_address(true), err);
-		}
+
+		error_code err; // ignore errors here
+		s->sock->set_option(socket_acceptor::reuse_address(true), err);
+
 #if TORRENT_USE_IPV6
 		if (ep.protocol() == tcp::v6())
 		{