How to send multipart messages using libnl and generic netlink?

I'm trying to send a relatively big string (6Kb) through libnl and generic netlink, however, I'm receiving the error -5 (NL_ENOMEM) from the function nla_put_string in this process. I've made a lot of research but I didn't find any information about these two questions:

• What's the maximum string size supported by generic netlink and libnl nla_put_string function?
• How to use the multipart mechanism of generic netlink to broke this string in smaller parts to send and reassemble it on the Kernel side?

If there is a place to study such subject I appreciate that.