security: extend userdata for IPsec events

security: extend userdata for IPsec events

Extending 'userdata' to be used for IPsec events too.

IPsec events would have some metadata which would uniquely identify the
security session for which the event is raised. But application would
need some construct which it can understand. The 'userdata' solves a
similar problem for inline processed inbound traffic. Updating the
documentation to extend the usage of 'userdata'.

Signed-off-by: Anoob Joseph <anoob.joseph@caviumnetworks.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>