We call tap_sock_unix_new() to handle a new connection to the qemu socket
if we get an EPOLLIN event on c->fd_tap_listen. If we get an error event
on c->fd_tap_listen instead, we'll fall through to the "tap reset" path.
However, this won't do anything useful for an error on the listening
socket, it will just close the already connected socket. If we wanted to
handle errors on this socket, we'd need to do something different than for
an error on the connected socket.
So, change the logic to explicitly do nothing for any !EPOLLIN events on
the listening socket.
Signed-off-by: David Gibson