vsock/virtio: Rename virtio_vsock_skb_rx_put()

In preparation for using virtio_vsock_skb_rx_put() when populating SKBs
on the vsock TX path, rename virtio_vsock_skb_rx_put() to
virtio_vsock_skb_put().

No functional change.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>