If socket's error queue is not empty, EPOLLERR must be set. Otherwise,
reader of error queue won't detect data in it using EPOLLERR bit.
Currently for AF_VSOCK this is actual only with MSG_ZEROCOPY, as this
feature is the only user of an error queue of the socket.
Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>