mac80211: Deactivate mesh path timers when freeing nodes

Mesh paths are deleted via mesh_path_del() which properly
deactivates the timer associated to a mesh path.  But if paths were
deleted by mesh_table_free(..., true) timers would not be deactivated.
This fixes this case.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>