* implementation of the following ubus methods:
1. "get_sessions"
2. "clear_sessions"
3. "clear_session"
4. "get_bss_list"
* tracking of STA sessions and events (AUTH, ASSOC, etc.)
* caching of events is handled by hostapd and resides in
AVL until it is processed by ubus_collector
* added hard-coded caching limit to prevent memory leaks;
this should be made configurable at some point in the
future
Signed-off-by: Damir Franusic <damir.franusic@netexperience.com>
