[strongSwan] Augment the "esp cipher suites" with foreign not standard ciphers

[Martin Willi]

Hi Mugur,
> 
> need to support with strongSwan an "exotic" cipher implemented both by
> the NPU and the remote system.

Adding a new ESP cipher is possible, but not straight forward. You'll
need to add support in several layers:

- First, of course, the kernel needs support for this algorithm in the
  crypto API
- The kernel needs support for the new algorithm in the XFRM subsystem
- Choose an IKEv2 algorithm identifier (in private space?) for your
  algorithm
- Add a proposal configuration option for the algorithm identifier
- Extend the kernel interface by the new cipher


Regards
Martin