LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage
collection of C identifier name sections despite the __start_/__stop_
references. GNU ld before 2015-10 had the behavior as well. Simply set
the retain attribute so that GCC 11 (if configure-time binutils is 2.36
or newer)/Clang 13 will set the SHF_GNU_RETAIN section attribute to
prevent garbage collection.
Without the patch, there are linker errors with -z start-stop-gc
(LLD default) when -Wl,--gc-sections is used:
```
ld.lld: error: undefined symbol: __start___eap
>>> referenced by eap.c
>>> src/eap.o:(eap_init)
```
The remain attribute will not be needed if the metadata sections are
referenced by code directly.
The goal is to add specifically EAP-WSC registrar side and it looks like
extending our EAP and EAPoL code to support both supplicant and
authenticator-side methods is simpler than adding just EAP-WSC as a
special case.
Since EAP-WSC always ends in an EAP failure, I haven't actually tested
the success path.
Replace the usage of eap_send_response() in the method implementations
with a new eap_method_respond that skips the redundant "type" parameter.
The new eap_send_packet is used inside eap_method_respond and will be
reused for sending request packets in authenticator side EAP methods.
