bluetooth: controller: Add LLCP TX to tx_ack FIFO size

The MFIFO holding TX nodes on the ack path back to the host was only
sized to hold the possible number of ACL TX nodes. However, additional
TX nodes are allocated for LLCP and use the same FIFO.

By adding LLCP_TX_CTRL_BUF_COUNT to the size, the FIFO will be able to
hold the worst-case number of TX nodes.

Signed-off-by: Morten Priess <mtpr@oticon.com>