Merging TranslateReturnCode into wolfSSL_LastError dropped the
IP_SOCK_getsockopt(SO_ERROR) lookup emNET integrations need to retrieve
the canonical IP_ERR_* for a failed recv/send, leaving a broken branch
that returned the raw value and mishandled the POSIX-facade convention.
Restore the historic lookup (fixing the optlen pointer-vs-int typo
along the way) and add a CI test that builds wolfSSL with
-DWOLFSSL_EMNET against a clean-room shim providing an emNET-faithful
IP_SOCK_getsockopt (SO_ERROR-then-errno fallback, since Linux does not
stash EAGAIN in SO_ERROR); recv/send fall through to glibc.
The emNET `wolfSSL_LastError` branches were incorrect. The second one
was never hit and would never compile. The first one inverts error codes
that should not be inverted.
This fixes that code and adds a test with a shim layer to test emNET
calls without using emNET.
Andrew Hutchings