Bluetooth: Connection parameters check helper

This patch renames l2cap_check_conn_param() to hci_check_conn_params()
and moves it to hci_core.h so it can reused in others files. This helper
will be reused in the next patch.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
WIP: Bluetooth: LE Connection Parameter Update Procedure

This patch adds support for Connection Parameters Request Link Layer
control procedure.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Export slave latency parameter

This patch exports slave latency parameter through Bluetooth debugfs
interface. The default value is 0 and it may be changed by writing the
new value in conn_latenty file. The acceptable values range from 0x0000
to 0x01F3, according described in Core 4.1, Vol 2, 7.8.12.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Export supervision timeout parameter

This patch exports supervision timeout parameter through Bluetooth
debugfs interface. The default value is 0x002a and it may be changed by
writing the new value in conn_supervision_timeout file. The acceptable
values range from 0x000a to 0x0c80 according described in Core 4.1,
Vol 2, 7.8.12.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Bluetooth: Extend hci_conn_params

This patch adds slave latency and supervision timeout parameters to
hci_conn_params struct.

During connection establisment, we save these values in hci_conn
(as we do with min and max connection interval) so we are able to know
what values the connection is currently using.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>