This patch increases the receive buffer size to HCI_MAX_FRAME_SIZE
which improves the RX throughput considerably.

Tested against BRM/Atheros/CSR USB Dongles with PAN profile using
iperf and chariot. This gave significant (around 40%) increase
in performance (increased from 0.8 to 1.5 Mb/s in Sheld room)
Signed-off-by: NVikram Kandukuri <vikram.kandukuri@atheros.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>