disconnect by server, propagate accept event

disconnect by server: user can force disconnect of client
accept event: user receive accept event to make some actions on it. e.g:
timeout to disconnect client
releasing allocated memmory
removed not needed code
one too many deleted
handling server disconnect if client disconnect already happened
propagate disconnect event to user code

propagate disconnect event to user code
can be used to disable timeout for server disconnect
removed not needed demo-ble.c
- minor changes to pull request (use SIGHUP to signal disconnect, hci_disconnect to disconnect