writeCommandPacketUint32: fix packet length comment
writeCommandPacketUint32: fix packet length comment

roth1002/mysql,rlowe/mysql,Frca/mysql,rafaeljusto/mysql,eklitzke/mysql,siriele/mysql,helight/helight_code,VividCortex/mysql,netroby/mysql,helight/helight_code,nanata1115/mysql,Freeaqingme/golang-sql-driver-mysql,tmulchay/mysql,LightKool/mysql-go,sunjian1/mysql,bookerzzz/mysql,jockchou/mysql,yyljlyy/mysql,LightKool/mysql-go,helight/helight_code,methane/mysql,helight/helight_code,henrylee2cn/mysql,helight/helight_code,methane/mysql,hyperworks/mysql,VividCortex/mysql,springning/mysql,beego/mysql,cw2018/mysql,go-sql-driver/mysql,zhgo/mysql,cxflag203/mysql,dalinaum/go-mysql-driver,segmentio/mysql,helight/helight_code,wfxiang08/mysql,muthusubbu459/mysql,yonglehou/mysql,helight/helight_code,helight/helight_code,Go-SQL-Driver/MySQL,bookerzzz/mysql,helight/helight_code,hebihui/mysql,eXcomm/gomysql,segmentio/mysql,aperera/mysql,chinanjjohn2012/mysql,Vorstack/mysql,joshuaprunier/mysql