sk-inet: More detailed error parsing on unconnected socket

errno is no guaranteed to be clear if call exit with
success. Thus make sure we've ret negative here and
test for errno then.

http://bugzilla.openvz.org/show_bug.cgi?id=2412



Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>