tetragon: Fix generated_syscalls list

Currently we do not inlcude sys prefix in generated syscall list,
so the list fails validation and the spec like this one fails:

  spec:
    lists:
    - name: "all-syscalls"
      type: "generated_syscalls"
    kprobes:
    - call: "list:all-syscalls"

Adding missing "sys_" prefix.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

pkg/btf/validation.go

@@ -501,7 +501,7 @@ func GetSyscallsList() ([]string, error) {
 	}
 	for _, value := range names {
 		var fn *btf.Func
-		sym, err := arch.AddSyscallPrefix(value)
+		sym, err := arch.AddSyscallPrefix(fmt.Sprint("sys_", value))
 		if err != nil {
 			return []string{}, err
 		}