[meshcop] set message offset when sending JOIN_FIN.rsp (#3516)
[meshcop] set message offset when sending JOIN_FIN.rsp (#3516)


turon/openthread,chshu/openthread,bukepo/openthread,openthread/openthread,librasungirl/openthread,lanyuwen/openthread,chshu/openthread,bukepo/openthread,turon/openthread,jwhui/openthread,librasungirl/openthread,chshu/openthread,erja-gp/openthread,abtink/openthread,jwhui/openthread,erja-gp/openthread,srickardti/openthread,openthread/openthread,lanyuwen/openthread,chshu/openthread,openthread/openthread,chshu/openthread,erja-gp/openthread,srickardti/openthread,lanyuwen/openthread,abtink/openthread,librasungirl/openthread,openthread/openthread,srickardti/openthread,turon/openthread,erja-gp/openthread,abtink/openthread,jwhui/openthread,lanyuwen/openthread,bukepo/openthread,abtink/openthread,erja-gp/openthread,lanyuwen/openthread,librasungirl/openthread,erja-gp/openthread,srickardti/openthread,lanyuwen/openthread,turon/openthread,bukepo/openthread,chshu/openthread,jwhui/openthread