Proper follow-up for Bug#12762885 - 61713: MYSQL WILL NOT BIND TO "LOCALHOST"

IF LOCALHOST IS BOTH IPV4/IPV6 ENABLED.

The original patch removed default value of the bind-address option.
So, the default value became NULL. By coincedence NULL resolves
to 0.0.0.0 and ::, and since the server chooses first IPv4-address, 
0.0.0.0 is choosen. So, there was no change in the behaviour.

This patch restores default value of the bind-address option to "0.0.0.0".

mysql-test/r/mysqld--help-notwin.result

@@ -747,7 +747,7 @@ autocommit TRUE
 automatic-sp-privileges TRUE
 back-log 50
 big-tables FALSE
-bind-address (No default value)
+bind-address 0.0.0.0
 binlog-cache-size 32768
 binlog-direct-non-transactional-updates FALSE
 binlog-format STATEMENT

mysql-test/r/mysqld--help-win.result

@@ -755,7 +755,7 @@ autocommit TRUE
 automatic-sp-privileges TRUE
 back-log 50
 big-tables FALSE
-bind-address (No default value)
+bind-address 0.0.0.0
 binlog-cache-size 32768
 binlog-direct-non-transactional-updates FALSE
 binlog-format STATEMENT

sql/mysqld.cc

@@ -341,7 +341,7 @@ static char *default_character_set_name;
 static char *character_set_filesystem_name;
 static char *lc_messages;
 static char *lc_time_names_name;
-static char *my_bind_addr_str;
+char *my_bind_addr_str;
 static char *default_collation_name;
 char *default_storage_engine;
 static char compiled_default_collation_name[]= MYSQL_DEFAULT_COLLATION_NAME;
@@ -1841,9 +1841,6 @@ static void network_init(void)
     struct addrinfo *ai, *a;
     struct addrinfo hints;
 
-    if (!my_bind_addr_str)
-      my_bind_addr_str= (char *) "0.0.0.0";
-
     sql_print_information("Server hostname (bind-address): '%s'; port: %d",
                           my_bind_addr_str, mysqld_port);
 
@@ -5713,9 +5710,6 @@ struct my_option my_long_options[]=
   {"autocommit", 0, "Set default value for autocommit (0 or 1)",
    &opt_autocommit, &opt_autocommit, 0,
    GET_BOOL, OPT_ARG, 1, 0, 0, 0, 0, NULL},
-  {"bind-address", OPT_BIND_ADDRESS, "IP address to bind to.",
-   &my_bind_addr_str, &my_bind_addr_str, 0, GET_STR,
-   REQUIRED_ARG, 0, 0, 0, 0, 0, 0},
   {"binlog-do-db", OPT_BINLOG_DO_DB,
    "Tells the master it should log updates for the specified database, "
    "and exclude all others not explicitly mentioned.",

sql/mysqld.h

@@ -146,6 +146,7 @@ extern char *opt_backup_history_logname, *opt_backup_progress_logname,
 extern const char *log_output_str;
 extern const char *log_backup_output_str;
 extern char *mysql_home_ptr, *pidfile_name_ptr;
+extern char *my_bind_addr_str;
 extern char glob_hostname[FN_REFLEN], mysql_home[FN_REFLEN];
 extern char pidfile_name[FN_REFLEN], system_time_zone[30], *opt_init_file;
 extern char default_logfile_name[FN_REFLEN];

sql/sys_vars.cc

@@ -308,6 +308,11 @@ static Sys_var_charptr Sys_basedir(
        READ_ONLY GLOBAL_VAR(mysql_home_ptr), CMD_LINE(REQUIRED_ARG, 'b'),
        IN_FS_CHARSET, DEFAULT(0));
 
+static Sys_var_charptr Sys_my_bind_addr(
+       "bind_address", "IP address to bind to.",
+       READ_ONLY GLOBAL_VAR(my_bind_addr_str), CMD_LINE(REQUIRED_ARG),
+       IN_FS_CHARSET, DEFAULT("0.0.0.0"));
+
 static Sys_var_ulong Sys_binlog_cache_size(
        "binlog_cache_size", "The size of the transactional cache for "
        "updates to transactional engines for the binary log. "