bonding: unify all places where actor-oper key needs to be updated.

actor_admin, and actor_oper key is changed at multiple locations in
the code. This patch brings all those updates into one location in
an attempt to avoid possible inconsistent updates causing LACP state
machine to go in weird state.

The unified place is ad_update_actor_key() with simple state-machine
logic -
  (a) If port is "duplex" then only it can participate in LACP
  (b) Speed change reinitializes the LACP state-machine.

Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>