socket: fix potential double close (#2663)

`_fd` should be reset if `ResetFileDescriptor` is going to return -1,
otherwise the fd will be closed in callers like `CheckConnectedAndKeepWrite`
or `Server::StartInernal` and socket lifecycle methods like `BeforeRecycled`
or `WaitAndReset`.

src/brpc/socket.cpp

@@ -594,6 +594,7 @@ int Socket::ResetFileDescriptor(int fd) {
     // Make the fd non-blocking.
     if (butil::make_non_blocking(fd) != 0) {
         PLOG(ERROR) << "Fail to set fd=" << fd << " to non-blocking";
+        _fd.store(-1, butil::memory_order_release);
         return -1;
     }
     // turn off nagling.