@stangri The drivers I need are the ones in the picture and I don't think there is a kmod available for it, that's why I use the toolchain, but I can be wrong!
The way I am adding them is using make kernel_menuconfig
For anyone else looking at this - yes You could compile some modules that way not officially packaged, but keep in mind, the recipe uses unpatched kernel sources. So if You really need this to work, do not forget to apply patches from target/generic dir from OpenWrt tree for that particular SDK version and particular target You are using.
This will be rather hacky approach (normally You setup repository with packages You built with SDK) but it's faster.
Download the Image Builder from the same directory You downloaded SDK and unpack it. Create files dir in it, change to that dir and extract the kmod-netxen-nic package, so that You'll see etc and lib dirs with its content. Now go to root directory of Image Builder and make help to see what can be done. Check wiki: https://openwrt.org/docs/guide-user/additional-software/imagebuilder if You're still confused. Small hint: by default IB won't add LuCi to the image, so preferably add luci to PACKAGES. After writing firmware to Your device, You should be able to use opkg to install available packages.
@tmn505@stangri guys I can't thank you enough for your help, you just made my day... Finally I have it up and running.
Btw does it hurt to add more packages than the default ones, I added luci and luci-ssl?
You may also want to set the CONFIG_TARGET_KERNEL_PARTSIZE=128 CONFIG_TARGET_ROOTFS_PARTSIZE=2000 variables on the make image line to set custom partition sizes for kernel and rootfs, depending on the storage available on your x86_64 system (so obviously not those exact numbers).
I add things like luci-app-https-dns-proxy and luci-app-simple-adblock of course and when you have time you may want to look up uci-defaults and create a script to customize your install.