selftests: bonding: add ipsec offload test

This introduces a test for IPSec offload over bonding, utilizing netdevsim
for the testing process, as veth interfaces do not support IPSec offload.
The test will ensure that the IPSec offload functionality remains operational
even after a failover event occurs in the bonding configuration.

Here is the test result:

TEST: bond_ipsec_offload (active_slave eth0)                        [ OK ]
TEST: bond_ipsec_offload (active_slave eth1)                        [ OK ]

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20250925023304.472186-2-liuhangbin@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>