Bluetooth: tester: Support general and limited discoverable for classic

Disable discoverable mode if `cp->discoverable` is
`BTP_GAP_NON_DISCOVERABLE`.

Set general discoverable mode if `cp->discoverable` is
`BTP_GAP_GENERAL_DISCOVERABLE`.

Set limited discoverable mode if `cp->discoverable` is
`BTP_GAP_LIMITED_DISCOVERABLE`.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>