Make BIO_sock_error return a proper error code when getsockopt fails

BIO_sock_error() returned 1 when getsockopt() fails when it should
return the error code for that failure.

Additionally, the optlen parameter to getsockopt() has to point at
the size of the area that the optval parameter points at rather than
zero.  Some systems may forgive it being zero, but others don't.

Reviewed-by: Matt Caswell <matt@openssl.org>