Merge branch 'xfrm & bonding: Correct use of xso.real_dev'

Cosmin Ratiu says:

====================
This patch series was motivated by fixing a few bugs in the bonding
driver related to xfrm state migration on device failover.

struct xfrm_dev_offload has two net_device pointers: dev and real_dev.
The first one is the device the xfrm_state is offloaded on and the
second one is used by the bonding driver to manage the underlying device
xfrm_states are actually offloaded on. When bonding isn't used, the two
pointers are the same.

This causes confusion in drivers: Which device pointer should they use?
If they want to support bonding, they need to only use real_dev and
never look at dev.

Furthermore, real_dev is used without proper locking from multiple code
paths and changing it is dangerous. See commit [1] for example.

This patch series clears things out by removing all uses of real_dev
from outside the bonding driver.
Then, the bonding driver is refactored to fix a couple of long standing
races and the original bug which motivated this patch series.

[1] commit f8cde9805981 ("bonding: fix xfrm real_dev null pointer
dereference")

v2 -> v3:
Added a comment with locking expectations for real_dev.
Removed unnecessary bond variable from bond_ipsec_del_sa().
v1 -> v2:
Added missing kdoc for various functions.
Made bond_ipsec_del_sa() use xso.real_dev instead of curr_active_slave.
====================

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>