Bluetooth: Controller to Host data flow control ACL Rx Count limited to 1

[cvinayak]

Describe the bug

BT_BUF_HCI_ACL_RX_COUNT introduced in #83774 is ending up being 1

BT_BUF_HCI_ACL_RX_COUNT should be allowed to be greater than or equal to 1, so that more number of ACL buffers be buffered up for host processing (in bursts, x bps) to match the reception over transport (in bursts, y bps).

At the same time, BT_BUF_ACL_RX_COUNT_EXTRA be for L2CAP recombination, so that BT_BUF_HCI_ACL_RX_COUNT is available for ACL buffer with and without Controller to Host data flow control.

Originally posted by @cvinayak in #83774 (comment)

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