Fix for Bluetooth device name reset to default name after reboot

Fix for Bluetooth device name reset to default name after reboot

Reason: When the BT device name is updated is getting saved
to the config data pointer but not to the persistent data
(i.e. bt_config.conf). So, when the reboot is happening it
is not able to get the updated device name from the persistent
data (i.e. bt_config.conf) as during reboot bt_config_flush is
not called. It is only called on the BT Enable Event.

Fix: Saving the BT Device name to persistent data using
btif_config_flush once it is set.

Tracked-On: OAM-67917

Signed-off-by: Gaganpreet kaur <gaganpreetx.kaur@intel.com>
Signed-off-by: Aiswarya Cyriac <aiswarya.cyriac@intel.com>