Destroy TCP connections before modules

This fixes a possible double-free during shutdown.

The issue was that the `tls_mgm` module was unloaded (free'ing all of
its "domains") before the connections were destroyed. This left
connections with dangling pointers to the domains, and when the
connections are cleaned up, if the reference count is 0, `tls_mgm`
can then try to free the domain again, causing a crash.

The solution is to defer `destroy_modules()` until after
`tcp_destroy()`.

It is possible that there are other related bugs that could be solved
in the same way (i.e. that `destroy_modules()` should move even further
down) but I've tried to be conservative.

Author: jes

shutdown.c

@@ -58,9 +58,9 @@ void cleanup(int show_status)
 #endif
 
 	handle_ql_shutdown();
-	destroy_modules();
 	udp_destroy();
 	tcp_destroy();
+	destroy_modules();
 	destroy_timer();
 	if (shm_memlog_size)
 		shm_mem_disable_dbg();