char: fix avail_connections init in qemu_chr_open_eventfd()

char: fix avail_connections init in qemu_chr_open_eventfd()

When trying to use a ivshmem server with qemu, ivshmem init code tries to
create a CharDriverState object for each eventfd retrieved from the server.
To create this object, a call to qemu_chr_open_eventfd() is done.
Right after this, before adding a frontend, qemu_chr_fe_claim_no_fail() is
called.
qemu_chr_open_eventfd() does not set avail_connections to 1, so no frontend can
be associated because qemu_chr_fe_claim_no_fail() makes qemu stop right away.

This problem comes from 456d60692310e7ac25cf822cc1e98192ad636ece
"qemu-char: Call fe_claim / fe_release when not using qdev chr properties".

Fix this, by setting avail_connections to 1 in qemu_chr_open_eventfd().

Signed-off-by: David Marchand <david.marchand@6wind.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>