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>

mysql-test/suite/rpl/r/rpl_parallel_optimistic.result

@@ -626,6 +626,7 @@ include/save_master_gtid.inc
 connection server_2;
 include/sync_with_master_gtid.inc
 connection server_2;
+SET @org_log_warnings=@@GLOBAL.LOG_WARNINGS;
 set global log_warnings=2;
 BEGIN;
 INSERT INTO t1 SET a=1;
@@ -651,7 +652,7 @@ connection server_2;
 include/sync_with_master_gtid.inc
 connection server_2;
 include/stop_slave.inc
-set global log_warnings=default;
+set global log_warnings=@org_log_warnings;
 SET GLOBAL slave_parallel_mode=@old_parallel_mode;
 SET GLOBAL slave_parallel_threads=@old_parallel_threads;
 include/start_slave.inc