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>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>