optimize memory issues (#767)

* optimize memory issues

1. introduce jemalloc support, which can dump current memory usage
2. reduce the GlobalEvent broadcaster memory usage.
3. reduce tcp & udp tunnel memory usage

TODO: if peer conn tunnel hangs, the unbounded channel of peer rpc
may consume lots of memory, which should be improved.

* select a port from 15888+ when port is 0

easytier/src/tunnel/common.rs

@@ -159,7 +159,7 @@ where
             reserve_buf(
                 &mut self_mut.buf,
                 *self_mut.max_packet_size,
-                *self_mut.max_packet_size * 32,
+                *self_mut.max_packet_size * 2,
             );
 
             let cap = self_mut.buf.capacity() - self_mut.buf.len();