fatal error: netlink/genl/genl.h: No such file or directory

You can search the correct package with this command:

apt-file search /netlink/genl/genl.h

In my case the output is:

libnl-3-dev: /usr/include/libnl3/netlink/genl/genl.h

This means, I have to install the package libnl-3-dev:

sudo apt-get install libnl-3-dev

And you need libnl-genl-3-dev

sudo apt-get install libnl-genl-3-dev

Then open the config file:

nano hostap/hostapd/.config

and uncomment the line:

CONFIG_LIBNL32=y

Start make again.