vsock: Fix IOCTL_VM_SOCKETS_GET_LOCAL_CID to check also transport_local

Support returning VMADDR_CID_LOCAL in case no other vsock transport is
available.

Fixes: 0e12190 ("vsock: add local transport support in the vsock core")
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://patch.msgid.link/20250703-vsock-transports-toctou-v4-3-98f0eb530747@rbox.co
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: mmhal

net/vmw_vsock/af_vsock.c

@@ -2581,6 +2581,8 @@ static long vsock_dev_do_ioctl(struct file *filp,
 		cid = vsock_registered_transport_cid(&transport_g2h);
 		if (cid == VMADDR_CID_ANY)
 			cid = vsock_registered_transport_cid(&transport_h2g);
+		if (cid == VMADDR_CID_ANY)
+			cid = vsock_registered_transport_cid(&transport_local);
 
 		if (put_user(cid, p) != 0)
 			retval = -EFAULT;