[ upstream commit c861775 ]

Due to changes in newer kernels and the cilium/ebpf library, XDP
programs will in future be loaded as ebpf.AttachXDP. However, older
Cilium versions will have already created links with ebpf.AttachNone
programs. The kernel does not allow us to change the program of a link
if its attach type does not match.

This means that we can only use the new XDP attach type when a link is
newly created. This commit adds logic which detects errors on link
update and attempts to load and attach with the other attach type
instead. So when upgrading from an older version to a newer version,
new links are created as XDP attach type, but existing links will remain
using the AttachNone. On downgrade, all links will be created with
AttachNone, and existing links will continue to use AttachXDP.

Signed-off-by: Dylan Reimerink <dylan.reimerink@isovalent.com>
Co-authored-by: Timo Beckers <timo@isovalent.com>
Signed-off-by: Timo Beckers <timo@isovalent.com>

This commit is unique to release branches. ebpf-go will now return
AttachXDP as the attach type of XDP programs by default. This is something
the Cilium versions that want to upgrade to/from versions using the new
ebpf-go release need to be aware of.

This commit restores the old behaviour of the library on top of having the
retry loop added in the previous commit, making sure we don't use the new
attach type unless strictly necessary.

Signed-off-by: Timo Beckers <timo@isovalent.com>