If no data has been processed during recvmsg, return the error code.
This covers all errors received during non-AIO operations.

If any error occurs during a synchronous operation in addition to
-EIOCBQUEUED or -EBADMSG (like -ENOMEM), it should be relayed to the
caller.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>