Ignore socket options not supported by LWIP

Ignore socket options not supported by LWIP

For IP_RECVERR never returning the error structures that the option
enables is a valid implementation. A proper implementation would require
changes to the LWIP codebase. For TCP_FASTOPEN, it would only improve
the latency and therefore we can safely ignore the option.

Signed-off-by: Marco Schlumpp <marco@unikraft.io>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Reviewed-by: Mihnea Firoiu <mihneafiroiu0@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
GitHub-Closes: #46