[connman] inotify: fix buffer size

Fix buffer to which inotify events are read to be large enough,
according to inotify(7) manual page.
[connman] inotify: refcount struct connman_inotify

When processing inotify events, callbacks may unregister which can
result in freeing the related connman_inotify struct. However that
struct is referenced in the loop which processes the events read in.

Implement reference counting to make sure the structure is available
while events are being processed.