bugs/known/: mention issue #160, bnx2 firmware files in initramfs/netboot packages

Updated netboot packages for Grml 2020.06 have been uploaded:

* grml_netboot_package_grml32-full_2020.06.tar.bz2
* grml_netboot_package_grml32-full_2020.06.tar.bz2.sha1
* grml_netboot_package_grml32-full_2020.06.tar.bz2.sha1.asc
* grml_netboot_package_grml64-full_2020.06.tar.bz2
* grml_netboot_package_grml64-full_2020.06.tar.bz2.sha1
* grml_netboot_package_grml64-full_2020.06.tar.bz2.sha1.asc

Closes: https://github.com/grml/grml/issues/160