doc: explain why struct_ops uses ignoreExtra

Co-authored-by: Lorenz Bauer <[email protected]>
Signed-off-by: Eishun Kondoh <[email protected]>

Author: shun159

elf_reader.go

@@ -1519,6 +1519,7 @@ func init() {
 		// This has been in the library since the beginning of time. Not sure
 		// where it came from.
 		{"seccomp", sys.BPF_PROG_TYPE_SOCKET_FILTER, 0, _SEC_NONE},
+		// Override libbpf definition because we want ignoreExtra.
 		{"struct_ops+", sys.BPF_PROG_TYPE_STRUCT_OPS, 0, _SEC_NONE | ignoreExtra},
 		{"struct_ops.s+", sys.BPF_PROG_TYPE_STRUCT_OPS, 0, _SEC_SLEEPABLE | ignoreExtra},
 	}, elfSectionDefs...)