MDEV-33582 Add more warnings to be able to better diagnose network issues

Warnings are added to net_server.cc when
global_system_variables.log_warnings >= 4.

When the above condition holds then:
- All communication errors from net_serv.cc is also written to the
  error log.
- In case of a of not being able to read or write a packet, a more
  detailed error is given.

Other things:
- Added detection of slaves that has hangup to Ack_receiver::run()
- vio_close() is now first marking the socket closed before closing it.
  The reason for this is to ensure that the connection that gets a read
  error can check if the reason was that the socket was closed.
- Add a new state to vio to be able to detect if vio is acive, shutdown or
  closed. This is used to detect if socket is closed by another thread.
- Testing of the new warnings is done in rpl_get_lock.test
- Suppress some of the new warnings in mtr to allow one to run some of
  the tests with -mysqld=--log-warnings=4. All test in the 'rpl' suite
  can now be run with this option.
 - Ensure that global.log_warnings are restored at test end in a way
   that allows one to use mtr --mysqld=--log-warnings=4.

Reviewed-by: <serg@mariadb.org>,<brandon.nesterenko@mariadb.com>

sql/semisync_master_ack_receiver.h

@@ -228,6 +228,11 @@ public:
     return m_fds[slave->m_fds_index].revents & POLLIN;
   }
 
+  bool is_socket_hangup(const Slave *slave)
+  {
+    return m_fds[slave->m_fds_index].revents & POLLHUP;
+  }
+
   void clear_socket_info(const Slave *slave)
   {
     m_fds[slave->m_fds_index].fd= -1;
@@ -296,6 +301,11 @@ public:
     return FD_ISSET(slave->sock_fd(), &m_fds);
   }
 
+  bool is_socket_hangup(const Slave *slave)
+  {
+    return 0;
+  }
+
   bool has_signal_data() override
   {
     return FD_ISSET(local_read_signal, &m_fds);