Revert "chardev: tcp: postpone async connection setup"

Revert "chardev: tcp: postpone async connection setup"

This reverts commit 25679e5d58e258e9950685ffbd0cae4cd40d9cc2.

This commit broke "reconnect socket" chardev that are created after
"machine_done": they no longer try to connect. It broke also
vhost-user-test that uses chardev while there is no "machine_done"
event.

The goal of this patch was to move the "connect" source to the
frontend context. chr->gcontext is set with
qemu_chr_fe_set_handlers(). But there is no guarantee that it will be
called, so we can't delay connection until then: the chardev should
still attempt to connect during open(). qemu_chr_fe_set_handlers() is
eventually called later and will update the context.

Unless there is a good reason to not use initially the default
context, I think we should revert to the previous state to fix the
regressions.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180817135224.22971-3-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>