tests: reduce sleep interval in ikev2 sa rekey test

tests: reduce sleep interval in ikev2 sa rekey test

Type: test

The sleep interval for this test is set to 0.1 seconds instead of
the default 2 seconds. This change is necessary because the test
verifies the expiration of old IPsec SAs
(self.fail("old IPsec SA not expired")) within a strict timeframe.
A longer sleep interval, such as 2 seconds, would significantly
delay the loop iterations, reducing the granularity of checks for
SA expiration and increasing the risk of false failures.

By setting the sleep interval to 0.1 seconds:
- The test can perform frequent checks for the status of IPsec SAs
- It reduces the likelihood of the test prematurely failing

Change-Id: I92ac3de0f33838620b51083d240043e62f37c490
Signed-off-by: Ivan Ivanets <[email protected]>