[MAC80211]: add sta_notify callback

This patch adds sta_notify callback and removes sta_table_notification
which was not used by any driver.
sta_notify() is essential for drivers that keeps notion of station
internally and need to be notified about removal or addition of a station
to the (I)BSS or assocation to an AP.

This version adds interface id to the parameter list
as suggested by Johannes Berg

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>