tests/sys/kern/ssl_sendfile: double timeouts for :grow and :truncate

[ngie]

Summary

The :grow and :truncate testcases fail semi-regularly in CI with
timeouts. Double the timeout to reduce false positives with the tests.

MFC after: 1 week

Test Plan

I ran this diff ~4,000 times with varying degrees of CPU usage, buildworld in the background, etc, without incidence.