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: 0e121905 ("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>