Attempt to fix broken sigpipe

```
Thread 1 "rtorrent main" received signal SIGPIPE, Broken pipe.

0x00007ffff7b998a3 in torrent::SocketStream::write_stream (this=0x5556453e3590, buf=0x555649ee79b0, length=16384) at /root/build/rtorrent/libtorrent/src/net/socket_stream.h:94
```

libtorrent/src/net/socket_stream.h

@@ -91,7 +91,7 @@ SocketStream::write_stream(const void* buf, uint32_t length) {
  if (length == 0)
  throw internal_error("Tried to write to buffer length 0.");
 
- return ::send(m_fileDesc, buf, length, 0);
+ return ::send(m_fileDesc, buf, length, MSG_NOSIGNAL);
 }
 
 }