IPsec: add nth matching SPD entry outbound TCs

Add testcases with plain ipv4 forwarding with 1, 10, 100 and 1000 SPD
entries on outbound traffic in both directions both directions. Only
match the last SPD entry and process others before the matching entry.
Add testcases only without flow cache optimization.
Refactor the Python functions that add SPD entries:
- Unify the args in functions that add one and multiple entries.
- For multiple entries, add the ability to pass an object that will
handle how values in each iteration (i.e. for each entry) are modified.

Change-Id: I061922eec6acc75a4e115202c07e72d89bf1f4d3
Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>