The vsock callbacks .vhost_vsock_set_guest_cid and
.vhost_vsock_set_running are the only ones to be conditional
on #ifdef CONFIG_VHOST_VSOCK.  This is different from any other
device-dependent callbacks like .vhost_scsi_set_endpoint, and it
also broke when CONFIG_VHOST_VSOCK was changed to a per-target
symbol.

It would be possible to also use the CONFIG_DEVICES include, but
really there is no reason for most virtio files to be per-target
so just remove the #ifdef to fix the issue.

Reported-by: Dov Murik <dovmurik@linux.ibm.com>
Fixes: 9972ae31 ("build: move vhost-vsock configuration to Kconfig")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>