fix(IPsec): fix policy tests

Replace the hardcoded SPD inbound/outbound ranges with values derived
from test inputs.
Add the necessary routes now that the tunnel endpoints are not in the
same subnet. Also add ip neighbor entry on DUT2 for the same reason.
Also replace ipsec sa dump with show ipsec all in teardown of tests
where both SAs and SPDs are configured to improve troubleshooting.

Change-Id: I7d89a99fcf457a701c87bf6ac07364b62802677d
Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>