link: allow pinning uprobe multi links

I accidentally dropped the change to allow pinning uprobe multi from
Jiri's patch. This restores the functionality.

Signed-off-by: Lorenz Bauer <[email protected]>

Author: lmb

link/uprobe_multi.go

@@ -172,14 +172,6 @@ func (kml *uprobeMultiLink) Update(prog *ebpf.Program) error {
 	return fmt.Errorf("update uprobe_multi: %w", ErrNotSupported)
 }
 
-func (kml *uprobeMultiLink) Pin(string) error {
-	return fmt.Errorf("pin uprobe_multi: %w", ErrNotSupported)
-}
-
-func (kml *uprobeMultiLink) Unpin() error {
-	return fmt.Errorf("unpin uprobe_multi: %w", ErrNotSupported)
-}
-
 var haveBPFLinkUprobeMulti = internal.NewFeatureTest("bpf_link_uprobe_multi", "6.6", func() error {
 	prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
 		Name: "probe_upm_link",