Fixes to Coverity issues 84388, 84386, 84385

mysql_mon.c: Added back server state logging to Debug build.
query_classifier.cc: removed some extra debug code, cleaned up a bit function documentation.
mysql_client_server_protocol.h, mysql_backend.c, mysql_common.c: changed some variables to signed ones to enable checking of calculations in the code.
skygw_utils.cc: removed erroneous debug assertion.

utils/skygw_utils.cc

@@ -1412,7 +1412,6 @@ int simple_mutex_unlock(
                         err,
                         strerror(errno));
                 perror("simple_mutex : ");
-                ss_dassert(sm->sm_mutex.__data.__nusers >= 0);
         } else {
                 /**
                  * Note that these updates are not protected.