Bluetooth: GATT: Persist Client Features config only when paired

BLUETOOTH CORE SPECIFICATION Version 5.1 | Vol 3, Part G page 2405:

  'For clients with a trusted relationship, the characteristic value
  shall be persistent across connections. For clients without a
  trusted relationship the characteristic value shall be set to the
  default value at each connection.'

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>